I've shot it quite a bit (Ektar 25 and RG 25), and not ever seen any increase in grain. Most all of mine is or was frozen at one point too. Most recently shot it in 35mm about a year ago. I stocked up quite a bit before Ektar 100 was announced.
I have some old Ektar 125 that I shot a few weeks ago, I found that I needed to overexpose it by 1 full stop to get good results, and some of the roll had huge grain, and some did not. I have heard similar reports on Ektar 25. Overall I was really pleased with the shots that had "normal" Ektar grain, and some of the shots with the huge grain were not that bad. I can see why there is an artistic movement toward this kind of expired film look, but still it's not my thing.
If you want to see what Ektar 25 used to look like check out Flicker, there are people over there that have posted newly scanned photos from from negatives and photos shot when Ektar was a new film, and some that were shot on expired Ektar recently.
EdSawyer, Do you think you might want to trade a roll of that Ektar 25 for a roll of Ektar 125?