I certainly don't mind re-cycled art - if it is done well. If you look at 3.5 Rules Compendium, which ONLY contained re-cycled art, I never felt ripped off, because the art was re-used in a such a clever way (see the Enworld review for specifics).
What irks me about Arcane Power is that some of the art is re-used in a silly way. Take the Gatecrasher from 3.0 Manual of the Planes. Actually, he was already converted to 4E as a paragon path in 4E Manual of the Planes. Except the picture they used there showcased the rogue-as-striker meme, smashing a rakasha's head with a hammer. Not that I minded too much, though I wondered why that was, as an image, more exemplifying of the gatecrasher (prestige) class than a bunch of keys and lock picks - referring here to the image in 3.0 Manual of the Planes.
Imagine the surprise when I saw that very image used in Arcane Power - to illustrate the Arcane Wayfarer (aka Wayfarer Guide in 3.5 Complete Arcane). [Btw, this is from memory - I didn't buy the book.]
How silly! Keys and lock picks have nothing to do with magic transport. They don't even have something to do with transport per se. They have something to do with - gate crashing.
So there you go. Not only can't WotC pay artists for new art work, they also can't pay someone able to re-cycle art with a modicum of, er, intelligence.
And to top it all, that picture is printed in the book with a wrong colour scheme. At the very least, the colours look like faded as if exposed to too much sun light. I should know, as I both own the 3.0 MotP and know the digital picture from the Arcane Power art gallery.
Ordinarily, I would have recommended people to buy the PDF instead (because WotC PDFs remind you - painfully - of how the printed art is intended to look like) - but, given how things are now, I'd recommend them to do something else. ... why, borrow the book from a friend of course!
To sum up. They re-use art, do so in an amateurish way, and print it cheaply. If that isn't indicative of how best-selling 4E is, I don't know what could be. Either that or they don't care to rip off customers in times when they are doing exceedingly well, financially. You decide!