Those are good points, especially about the resale. However all their new amps except the 33h now have detachable powercords. I own 436 amps which are monoblocks in the same powerrange as the 336, and the type of powercords used does make a difference. Some people might be relieved that they can update the powercord if you make the mod.
One could just open the 336, take loose the powercord by unscrewing it from the taps, buy about a foot of 10 guage stranded, flexible wire at Home Depot (I've used this for power cords and it sounds very good), connect it inside the amp, (be sure to note which taps the orginal wires (hot, nuetral, and ground, and draw a picture where they are all connected) , add the male IEC to the other end, and then you can experiment with other powercords to you ears' content. If you decide to sell the amp you can always reattach everything as before and your 336 would be "stock".
I would only attempt this if you have basic wiring skills or a friend familiar with electrical connections. As I recall once you have the cover off the 336, the powercord connections are really straight forward requiring average technical skill, but be sure to sketch the wiring arrangement so there is no doubt where to reattach everything when you get done.
Enjoy,
Sgr