You won't regret getting the 135/2... It's a really nice lens on FF. It would be nice if it had IS for use on crop sensor cameras... But it's hard to imagine any other improvements... And IS would add weight, size, cost and complexity.
Personally I think the 24/1.4 II is way, way overpriced. Big and heavy, too. I wish the 24/2.8 would get updated to USM, perhaps some optical tweaking and build more similar to the 28/1.8. But I might just pick up a decent used copy of it anyway.
It's sometimes true that lenses lose value when a new model is introduced. Other times not so much. The new 100L Macro H-IS is another example... It's so much more expensive that prices of used 100/2.8 USM haven't really gone down much.... Are actually only slightly less than what I paid for mine new some years ago.
Still, even if it happens that a new model comes out and the values of the older version drop significantly... What about all the photos you didn't make while waiting to see if something new might be introduced?
Have fun and be proud that with each and every purchase you are doing your part to help re-invigorate the global economy!