What you are going to see here are tons of very opinionated answers. Which is fine, just take it all with a giant grain of salt. Some advice will be and I think already is a little unbalanced.
Revives -- how big a mana pool do you have and how many do you really need? Do you have enigma to keep them from wandering off constantly in the first place? A single point will get even someone with pretty low level equipment a half dozen or more. There are probably better places to spend more points.
Curses -- They are far from valuable only because more points extend their duration. They cover more area. This is very valuable with dim vision. It's valuable with amplify too, but you have to ask yourself, do you want all the things you've dim-visioned to suddenly see you again if you cast a boosted amplify on what your army is fighting at the moment? You can only have one or the other at once. Since your army can only fight so many guys in so broad an area, there's a lot to be said for making amp a one-point wonder and, if you boost any curse, to boost dim vision instead of amplify.
Mages -- very useful as meatshields sometimes, but also get in the way quite a bit. Additionally, they die fairly quickly unless you have a ton of plus skills, and it takes a long time and a LOT of corpses to keep recasting them so you always get the cold and poison ones. You can get many bad and time-consuming runs of casting that don't get you what you want. The tediousness of trying to get the right mages shouldn't be understated -- this is a game, after all, and it's about fun in the end, not tedious busywork. Plus, when you run out of corpses and still can't get the poison mages and cold mages in sufficient number you want(remember they keep dying), it won't matter how many points you put in skeleton mages -- all of them will be unsatisfactory for the situation at hand.
Finally, the summoner is an extremely rebuildable character. You may not get your ideal build right away. It's probably pretty common that people don't. So if you want to experiment, go ahead. Just make your experiments coherent instead of little side trips here and there that all eventually add up to nothing. Get your main strengths, then some helper strengths that are still strong, and see how you like those helpers. The basic 20 in RS, SM, and CE will always be strong. If you're methodical and thoughtful, you can experiment a lot and refine your game over time and still enjoy characters who don't wind up to be precisely your favorite build in the end.