I think the biggest thing with obtaining skills isn"t so much picking one particular route as it is putting some variety into it.
In my ideal system you would have class hubs with trainers and so forth, which you can access (a mage tower for mages, a rogues den, necromancer coven, warriors training centre, etc). From here you can purchase your basic skills. You can also access a resource (it can be a trainer, a library, whatever) which will guide you in your quest for greater power. So once I hit a certain level I might find out that there is a tribe of monsters living in a certain zone who"s casters have the ability to conjure powerful elementals. So I can go to their zone, do a nice quest chain for them (preferably relevant to them teaching me the spell, and not just a random quest with it tacked onto the end), and they teach me how to summon elementals.
Or the trainer/library/whatever can tell me there"s a rumour that a powerful boss in a certain dungeon who"s spent his lifetime researching teleportation. So I go to this dungeon and as I"m there I come across pages from one of his books, drop off mobs, find them on the ground, whatever. Once I have all 10 pages or whatever I combine them together into a tome that I can use to learn how to teleport.
They don"t need to be as complex, don"t need a 2 hour quest chain for every new AoE or nuke. Some of them can just be one off drops, or require me to search out a trainer in an obscure location, or world drops, or crafted. The idea is to add some more immersion to character progression, stimulate the ingame economy, create a setup of class specific content and encourage players to explore out into different parts of the gameworld. While simultaneously through the trainer/class hub giving players the information they need to seek out their new skills so they don"t have to resort to resource websites.
It also helps differentiate between characters and increase replayability, since each class will have it"s own set of quest chains for it"s new major abilities as class specific content. Great for the roleplayers.
I think there"s just a lot of untapped potential when it comes to obtaining skills. I think the genre took a huge step back when we went from EQ"s scrolls to WoW"s trainers. Trainers kill a huge amount of class identity and sense of progression, going up to an interchangeable NPC, clicking a button, losing some gold and gaining a skill is so boring, it feels like a bit of a cop out.