1st class is certainly not necessary. It doesn't get you there any sooner. I have spent close to a hundred days traveling in Germany this century, all in 2nd class, and I have never felt it was inadequate. "Worth" the extra money? That is certainly a matter of choice. If you have more money than you know what to do with, why not? Or if you are very obese, and need the extra seat width, maybe then. Other than that - no.
As for reservations, I usually travel to small towns where there are only regional trains, which don't have reservations anyway, but on my latest_trip, I did use some Dauer-Speial tickets which I purchased online, and for which reservations were only €2 for each day's travel. I bought them, but I found I didn't need them.
I would wait until I was in Europe to get reservations; they're much less expensive there. Even on the one train I was on, in 2001, that was full, most of the seats were unreserved. I could have bought reservations just before train time and had a seat.
However, one word of warning: In high travel months (summer) Thalys trains to/from Brussels are often sold out for passholder reservation. (Thalys requires reservations for all travelers and limits them for railpass holders.) It might be wise to reserve Thalys trains when you arrive in Europe. However, Thalys trains are expensive, even with a railpass, and there are non-Thalys trains available.