rental cars in Amboise France and Eguishem France

Hi,
Yes, much easier to pick up in Tours - specifically in St Pierre des Corps, next to the TGV high-speed train station, which is where you are likely to arrive at.
As for the drive, it's indeed a bit long: did you already rule out Tours St Pierre des Corps -> Strasbourg by TGV train with a new car rental in Strasbourg? I guess you did. In that case, I can suggest Troyes as an interesting medieval city roughly half way.

I like the suggestion to take the train to Strasbourg and pick up a car there. If you have the time, I would stop in Beaune, Burgundy. It'd be lovely to be there at least two nights, we just stopped for one and it gave us a taste of the area. We then drove north out of Beaune on the Route des Grand Crus to Amboise.

The TGV to Strasbourg makes sense. thanks for the idea .

Is the TGV train direct from Tours to Strasbourg or do you have to change trains in Paris?

i misinterpreted the response. You might consider starting your trip in Strasbourg and then Eguisheim and then end in Loire/Tours

Whether breaking the trip or driving 7 hours in one day, I would keep the same car in preference to the extra paperwork and train ticket. Rick's France book covers more interim destinations such as Bourge, Beaune, and smaller towns along the wine route. The road via Troye looks a bit more direct, but Google Maps doesn't estimate much difference in drive time.

Yes, the route via Troyes and the route via Beaune / Burgundy are equivalent time wise. Via Troyes is quite a bit cheaper (fewer toll roads) but there is a stretch of slower road. Both Beaune and Troyes make for great stops. Along the Burgundy route, there's Vézelay, too, a bit further from the highway.
I would not recommend Bourges, because there is almost 100 miles of slow 2-lane road east of Bourges, whichever way you go.