Rail travel is part of the Europe experience.  Don’t give it all up.  Flying to Greece makes sense to me… maybe do the rest by rail.

But don’t jump on a pass until you’ve compared the options.   Could be that regular old tickets would be cheaper than a railpass.  Have a look at railsaver and Rick Steves rail webpages to decide whether a pass or tickets is better.

The train is faster than flying between many cities.  It’s also a lot more comfortable and convenient.  If the train ride is less than 5 hours, I take the train; between 5 and 7 hours, I do whichever is cheapest; over 7 hours, I fly unless it’s really expensive or an overnight train works out.
 
Look at a flexi or select pass instead of a consecutive day pass if you want to do a combination of train and plane. 

Keep in mind that the train is usually going to putyou in the center of the city.  Most Airports are many miles outside, and those miles can be expensive.