It's worth getting spells as you go along if you can. At least check out the traits and make sure you aren't skipping anything that gives a trait later. If you're burning I guess you can skip stuff but you're going to feel sheepish if someone asks you to set it and you don't have a level 25 spell that's easy to get.
Also keep in mind even if there are higher level spells that do the same thing, sometimes you'll be tight on points and the 2 points for sheep song vs 3 for other options (if you just want to set a sleep just in case) can make a difference.
Also while you are leveling some of them have nice stat boosts, even if you wouldn't necessarily cast them.
Anyway, do what you want. Is it worth getting as many spells as you can? In my opinion, yes. Can you live without a lot of them? For sure.
Edited, May 3rd 2013 11:09am by Olorinus
When it comes to sitting around not doing anything for long periods of time, only being active for short windows, and marginal changes and sidegrades I'd say FFXI players were the perfect choice for politicians.