Bear in mind you're asking my opinion while I'm posting as our website, which is always awkward, and Ross is still a Blue, (plus I don't want your admin thinking I'm only here to bump my comp) but the bottom line is he's a fabulous footballer, and can sit in the middle of the pitch passing it around all day long. He's everything you'd want out of a creative midfielder, with 2 good feet, and good vision, and if it was my decision to keep him, I would.
The problem I've found with Ross is that he can take too long to make a decision, i.e, shoot, or pass, and he doesn't get stuck in much in terms of attacking headers in the box etc, and prefers to hang back. Lukaku was a very static striker who stood in-between 2 defenders much of the time, and our movement up front was often dire, which didn't give Ross much to work with, which is why he'd often try to go alone.
I think a good manager could get inside his head and take him to the next level, and if I were Spurs I'd go full out to buy him, as your movement and pace is much better than ours, and he would shine,
as long as you used him as a provider, and not as an attacker.
Everton are looking at Sigurdsson, as opposed to Barkley, but I think they should be careful what they wish for, as Sigurdsson is the corner taker, free kick taker, and penalty taker, which improves his stats, but I'm not sure in open play he's as good as Ross, and according to an article by ESPN which you can read on our site if you wish, Ross more than doubled Sig's tally in chances created:
http://loveevertonforum.com/post/53029/thread
We've all gone through patches where we've doubted Ross, but now it looks like he's leaving, I'd worry we should have tried him for one more year with a new line up, but that could still happen.