Just a thought, but what if the boots of great speed were modified to have an effect similar to seven league boots? That is if, in addition to the speed boost of +30, they also reduced movement costs? That would certainly fit the idea of them being "of great speed", and would balance them relative to their doom+corrupt nature. The fact that they're an artifact would mean that they would have value over regular SLBs (due to immunity to destruction), even after factoring in the dooming and corrupting effects.
I think the bigger issue, though, is that with all the new corruptions being made, entry to the tree (and safer entry into the rift) will be made more difficult - and if it's that difficult to enter, then people just won't. I see three ways to resolve it:
1. Add more corruptions that can make it possible to enter.
2. Have some corruptions be guaranteed to show up within the corruption set.
3. Provide alternative ways to satisfy the requirements of entry.