Tiramisu,
In order to determine whether a Rail Pass or P-P tickets are a better value, you need to look at each of the rail trips you'll be taking and the cost for these. There's a small Map in the front of all Rick's Guidebooks that provides a quick "ballpark" method to calculate the cost of rail journeys.
One thing to mention about Rail Passes is that these don't include reservation fees, which are compulsory on virtually all of the "fast" trains such as the TGV in France. You'd have to pay these separately.
I never book seats or reservations in advance, as it's so easy to buy them in Europe (and often less expensive too!). Although there are enormous queues at ticket offices at times, I've never found that to be a problem. Most rail networks offer ticket machines now so that it's not necessary to stand in line. They're very easy to use.
The method I often use is to buy the tickets for my outgoing journey when I arrive in a city (since I'm at the station anyway). I research each of my rail trips on the net and have these listed on my Itinerary. That way I know the departure time and whether or not reservations will be required.
There are other options as well. In France you can visit an SNCF Boutique and buy your tickets there (for travel in France). They're located in different areas of Paris. In Italy I've also purchased tickets and reservations at local travel agents. I doubt that you'll have any trouble in Switzerland.
One point to note is that the automated ticket machines at Paris / CDG will only operate with the newer "chip" credit cards. Those that I saw in Italy recently would accept the older magnetic strip cards.
I'm sure one of the rail experts here will have some further comments.
Happy travels!