For point-to-point tickets there are advantages to going direct to the railway operator by buying tickets either at the train station or through their web site, especially if the site has English and works fairly easily, as those listed above tend to do. Advance-purchase discounts (most available starting 3 months before travel) can be significant, but will limit you to the travel dates and times you pre-select. There's no deadline to buy full-fare tickets, such as the 2nd-class rates summarized on Rick’s Train Travel Time & cost Map (and we think 2nd class is a fine way to travel).
Rail Europe is a US reseller and so applies there own exchange rate and issuing fees, but offers one-stop shopping for those departures you're committed to and also has the advance discounts for German and Italian tickets.
Is this still your travel plan, or has it changed? "2 adults and 4 kids, age 7-17.... spring 2016: Dresden, Prague, Munich/Fussen, Venice, and Rome." Are you flying into Berlin and out from Rome?
For the trip above, you'd only consider a 4-country Eurail Select Pass if you really wanted 1st class. Cost for each person 12 and older is $485, under 12 half that price, and 4 seat reservations about $50 per person. Prices for this pass may change in January.