I didn't read through this WHOLE thread (yet) but let me start by saying, that according to Pete Hines, the lowest settings on PC even, will either equal or still be better than the 360. He said you can't make the PC version look WORSE than the 360 version. I just read that on Twitter about 15 mins ago actually.
Secondly, on control schemes, a lot of PC gamers really like mouse/keyboard with their RPG's...however I do understand the controller preference some people have. I even prefer a controller sometimes. In fact I played both PC and 360 versions of Oblivion and I may have liked the controller better for that game. The thing for me is there seems to be a bit more freedom with the KB/Mouse. However, my point is, that even on the PC you can use your 360 controller (or even PS3). I just recieved in the mail the Microsoft Wireless controller adapter, which lets you use a wireless 360 controller on your PC. I just got it about 30 mins ago actually. Or you can use a wired one by simply plugging it up.
So, there really is no reason not to play PC version if you have a PC that can handle it. You get Mods, better graphics (or at least equal), freedom of control styles (whether you like KB/Mouse or controller)...and, not even mentioned but you can even still play with your large HDTV if you prefer. I hook my 40" Bravia to my computer sometimes when I want a bigger view.
So that's my thinking on the subject

Edit:
Something that came to me, I want to add. One thing that is BAD about mods is sometimes it will take away (like you said) from the game element itself. With Morrowind I got sidetracked by creating my own mods, adding items in the game, or creating my own race, or editing the look of a race, etc..that sometimes it took away from me actually enjoying the game. So from the aspect of early on, it might be better to just have a game you can just straight up play. Thing is..on the PC you can just ignore mods and just play the game. Later you may want to come back and play mods or whatever to extend the game. But still, something to consider.
As with Morrowind and Oblivion though, Mods extended the games life by several years. Yes some people played those games vanilla for years just fine..but others don't like to stay in the old engines and play..so mods allow them to "upgrade" those games to closer to a modern game..thus extending their life by several years.