If you purchase you tickets well ahead of time from the German Rail website, you can get a 1st class Europa-Spezial Tschechien fare as low as €29 pP one way to Prague, and you can print out the ticket on your home computer printer. If you do that, reservations are only €3 pP each way.
When I first went to Europe in the 1980s, my company made all the travel arrangements and paid for the tickets - all in 1st class. Then I went to Europe on my own and had a 2nd class rail pass. I didn't think the difference was worth the price difference. Then I went back on the company and bought my own tickets (with their money) and still used 2nd class. Since then, I have always ridden in 2nd class and never regretted it.
As for reservations, much of my travel is on lines only serviced by regional trains, which rarely have reservations. Only about 14 of my about 200 rail connections have been on express train. On the first 11 of these I never had reservations and only had to stand once, on a holiday, for ½ hour. When we got to the next station, some people got up and I was able to take their seats before the new people got on. I noticed that, although all seats were occupied, less than half were reserved.
On my last trip, I had three express legs, and, since reservations were only €2 when I bought the ticket online, I reserved. The reservations were never needed.
But, 1st class reservations are only €3 each when purchased with a ticket. At that price, why not get them and be sure?