I have become fully fluent in all the different kind of fare types etc (thank you MorganB for the SNCF booking post!) What I wondered though is whether there is a basic seasonality to train ticket prices, like with plane tickets. Is the best price you are going to get different at different times of the year (removing the variable of limited tickets maybe going faster at different times of the year). Thanks!

It depends on the country, I suppose. Here in Spain there are two different prices...winter and summer. But they don't change during the season , I mean, you don't buy them cheaper if you buy them in advance.

Ticket fare are absolutely not seasonal -- the full fare is the same all year long (quite simple: the fare is based on a rate per kilometer). But a lot more tickets are sold at promotional fares out of season rather than in season.

Thanks - sorry I posted with the France key word, but I realize I didn't specify France in the post itself!
Thanks kerouac - that answers my question!

France railpasses however often have off-season specials for travel fall and winter and this can make a pass a good deal when it may not normally be - so passes can be seasonal but not regular tickets though cheaper ones may be more available in off season. www.raileurope.com for pass prices.

In the UK prices aren't seasonal. Availability of cheap tickets depends on demand for higher priced tickets

again though in UK BritRail passes are discounted 25% for use between Nov 1 and Feb 28/29, making them more viable as ticket prices are static. (BR Off-Peak Passes)