@Rock-(View Post) If most peoples won't use it, why make it? If it would be too laggy, most peoples won't be able to open those saves, waste of time, if it has been rejected, it's for a reason. Code it yourself.
Keeping the workspace size constant makes Powder Toy run faster.
Turning XRES and YRES into variables (even with no possibility of changing them) decreases the frame rate by about 15% (this varied between 10% and 30% on the saves I tested, but 15% was the typical value).
Even if you keep the workspace the same size, just making resize possible makes Powder Toy run significantly slower.
I don't think making Powder Toy slower just to give the option of resizing is a good idea. Not to mention how much work would be involved in coding it...