i have the mod and yes its expensive but im glad i got it.
besides the metal housing protecting the lens, it makes it much stronger, so im not so worried about the plastic shrinking, deforming when focusing. i think it can take much more abuse.
you will need lens support. it does get heavy enough that i think itd rip out a m4/3 mount, and stress out an ef mount.
close focus at 3'7" rocks. you still need a diopter to achieve the nice bokeh i feel, but now ive got so much more flexibility.
i do think the weight and increased throw makes it become less of a one man crew lens when using it. and if youre using a follow focus, you need to use use a thick gear and a speed crank to take care of the long throw. metal focus gear on metal focus gear will make noise. (im looking for a rubber focus gear on my follow focus.) the front element extends long enough you can probably forget using a mattebox. but this is all how i feel about the 54 anyway. both a rehoused 36 and 54 are amazing lenses but in my opinion they still produce different results.
i also agree w tferradans in that i wouldnt have rented out the plastic version just because i dont think its robust enough. (i havent rented mine out yet and dont expect to until i figure out how to protect my investment in case someone says "it's lost").
and yes i think the resale value goes up. unless van diemen can crank out the mod in a week, youre not only reselling the lens, youre reselling the amount of time it took to get the mod in the first place which is a few months and seems like some people need/want the iscorama urgently enough to pay for it.
i say if you seriously get use out of your 36, shoot a lot, and you have friends/crew that can AC for you, then get it. i absolutely love mine, its on my camera 95% of the time.
if youre iscorama is nice and greased up, youre only shooting tests and youre a one man crew and really not using it that much, i dont think think the mod is worth that money.