To clarify, you'd be buying Skyrim on PC for 25$ and then adding mods?
If so, go for it man. From what I've seen, the modding community for Skyrim is off the hook, and I'm pretty sure you could have a good decade of fun with it. Plus, remembering the modding culture for Oblivion, I think you'll have active content for a good 4 years at least. That's more fun than Dawnguard can deliver IMO.