From the look of the samples on the Alienskin site, it does produce decent up sizing. I'm sure there can be instances where you can lose some detail, but like Paula mentions too, probably only noticable in print. They (Alienskin) are also offering a bundle of 3 products for 199, which if you have CS or higher, and you choose "Blow-up, Exposure, and Impact", you should be able to handle most any issue that crops up. Check out all the examples in these 3.

Illustrator already handles this issue with vector graphics which is incorporated into their "Smart Objects". You can create a base "?????.AI" (illustrator format) file which can be used within the Adobe Suite products, Re-size in either direction with no change in quality from the original.

My only thought is changing an original render, then trying to match to a Mask(alpha) render, it may not match perfectly even if you resize the Mask with the same plugin.  Yet there are lots of tricks to handling this situation too.

Good quality company, with a great track record. Usable with top notch packages.........Try the Demo, I'm going to.

___
Ockham's razor- It's that simple