I am taking the train from Berlin to Prague via Dresden. Is 1st class worth an extra 20 euros? What are the main differences btw 1st class and 2nd class on the EC trains? Thanks.

Same as with IC trains in your other thread.

IC and EC are the same type of trains, the only difference is that EC (EuroCity) trains cross borders. It might be a German or a Czech train, you never know.

In any case, 2nd class will be fine and spacious enough and you may sit in the restaurant car with either ticket. In 1st class you have about 20% more room and it is generally quieter (because of the business people riding here). However, 20€ aren't that much...

In First you will definitely have fewer seats in the same amount of space as in 2nd which usually adds at least one more seat. It will almost undoubtedly be less crowded although I've been on more than one First segment which had standing room only but a lot of that depended on time of day and route.

A lot of passholders may opt for First Class passes and there will be plenty of visitors in BOTH sections.