travel between Rhine/Mosel region and north end of wine road in France

"If you had 48 hours and were doing the wine culture later, where and how would you do this??"

Cochem is very pretty but quite small and deadly quiet before Easter. You'd be better in a larger city where there are things to do indoors as well as outdoors as the weather may be OK or it may still be pretty cold.

Mainz is a good choice. It's just 25 minutes from FRA and offers a lot to see and do. It's easy to navigate on foot and enjoyable as well due to the large network of pedestrians-only streets. Also, it's just south of the scenic Rhine Valley; from Mainz, take a train north and enjoy one of Germany's most scenic train routes, tour a castle, and visit an old-world village or two.

Market Square in Mainz
Old town in Mainz
Things to do in Mainz

Middle Rhine Valley castles
Middle Rhine Valley towns

Braubach and Marksburg Castle (best castle tour)
Bacharach

You can reach Strasbourg from Mainz in less than 2.5 hours if you use the 8:40 am train - figure a little longer at other hours. Cochem to Strasbourg would require 4-5 hours.

We just completed a trip to southern Germany and the Alsace area of France, starting from Frankfurt. We were some what disappointed with the mid-Rhine valley between Kobenz and Bingen in part because it was more brown than green (which may also be in March for your trip) and some what commercialized.We also thought that Mainz was just another German city with little tourist appeal. If you have a car - which I recommend if you can do it - I strongly recommend that you visit Rothenburg on der Tauber during that 48 hour time if you have never visited it before. It is one of Europe's best preserved towns, very historic and beautiful if you like that sort of thing even in the winter and early spring. It is about two hours from Frankfurt, can be visited in one day, and is about two and 1/2 hours to Strasbourg. Although a popular tourist spot, it should not be very crowded in March. Another good place for a short visit is Heidelberg which you could also possibly stop by on the way to Strasbourg after visiting Rothenburg.

A little less out of your way than Rothenburg ob der Tauber but still full of half-timbered charm but without the vast number of tourists would be Schwabisch Hall. I'd also recommend Heidelberg. It may be a little early in the year but we really enjoyed our drive along the German Wine Route south of the Rhein. You could also consider staying along the Rhein in Boppard, St. Goar or Bacharach then making the drive/train south in one day as it isn't really that far.

I strongly recommend that you visit Rothenburg on der Tauber during that 48 hour time if you have never visited it before. It is one of Europe's best preserved towns, very historic

It's one of Europe's most promoted preserved towns, but other than all the trinket shops, it isn't nearly as unique as advertised (strange that the poster found the Mittelrhein "somewhat commercialized", but gives Rothenburg a pass on the same measure). There are many, many options for preserved towns directly along the proposed route of travel. Just driving two and from Rothenburg would add four hours travel time.

Even though the Mittelrheintal is the most famous wine-producing region of Germany, the largest area of production is further upstream to the south. Some particularly good segments of the Rhine valley to explore for wine include the right bank stretch from Wiesbaden to Rüdesheim, and the both sides of the broad valley, from Darmstadt to Heidelberg on the right bank (known as the Bergstraße) and Worms to Landau on the left bank (known as the Deutsche Weinstraße). I'm partial to the Bergstraße, particularly the towns of Heppenheim and Weinheim, but mainly because I lived nearby for several years.

Large amounts of the land area between Bingen and Worms is occupied by vineyards as far as the eye can see, but in March, it will all look like a barren, treeless landscape.

A few thoughts on the Rhine and Rothenburg in winter...

"We just completed a trip to southern Germany and the Alsace area of France, starting from Frankfurt. We were some what disappointed with the mid-Rhine valley between Kobenz and Bingen in part because it was more brown than green (which may also be in March for your trip)"

In March the Rhine will absolutely be brown, just like everything else in Germany that isn't covered with evergreens. But the charm lies in the drama of the scenery, in the towns, and in the historic buildings. Even if you don't take a castle tour or walk through the old villages and only drive through, you'll still find winter scenes like this - http://static.panoramio.com/photos/large/4284798.jpg - and drive past buildings that look like this - http://micahcummings.com/blog/wp-content/uploads/2011/06/IMG_7363-950x633.jpg
But whether you visit the Rhine or R'burg you just can't expect winter to look like spring or summer.

"...and some what commercialized..."

The Rhine towns? This is a very puzzling comment. There is no place in Germany that can possibly compete with heavily "commercialized" Rothenburg! Even Rick admits, "Rothenburg is well on its way to becoming a medieval theme park."

"I strongly recommend that you visit Rothenburg on der Tauber during that 48 hour time if you have never visited it before. It is one of Europe's best preserved towns, very historic and beautiful... even in the winter and early spring."

Rothenburg has very attractive buildings but so do the Rhine towns, and buildings do not change from season to season; R'burg's winter landscape is as brown as elsewhere in Germany. IMO the primary difference between The Rhine and Rothenburg in winter is that Rothenburg is full of visitors year-round while the Rhine towns are mostly shuttered and lifeless. On the Rhine, the only real exception is Rüdesheim, which also gets year-round visitors. As far as spending the night goes, Rothenburg is probably better than Bacharach and most Rhine towns (which is the reason I suggested Mainz.)

Rothenburg by the way is much less "preserved" than "restored" since it was largely taken out in WW II:
https://commons.wikimedia.org/wiki/File:Rothenburg_ob_der_Tauber_Bomben_Zerst%C3%B6rung_Weltkrieg_1945.jpg

Rothenburg unfortunately doesn't offer anything like the Marksburg Castle tour. Marksburg is open year-round.

Mainz: Much of Mainz was flattened in WW II too, just like other German cities of any importance There is however a small but delightful old-world quarter, a very large pedestrian zone, and in winter, Mainz offers more fun things to do day and night than Rothenburg and Rüdesheim combined. If you merely drive through Mainz, or even just stopover at the main train station, you will probably get a very different impression, however - on the surface it DOES look skippable at first.

In short, I don't think a March visit to the Rhine is unreasonable at all as long as you stay in a place of some size (or maybe Rüdesheim) and do the Middle Rhine Valley on a day trip.

Thank you for a very interesting discussion of the advantages and disadvantages of visiting the Rhine area in March. Heidelburg sounds like it would be fun to visit, especially being home to 4 Universities; lots of young people. Realizing we will be basically landing and trying to recover from jet lag we will probably take the train to Strasbourg and save our Rhine exploration for another time. However you have sparked my interest in that area and I have enjoyed learning more about it. I think I'd rather see it during a "greener" season or maybe in fall color from a river cruise. So your comments have helped me make some choices and I thank you.