I just got this lip in the mail today. It's sort of a dull, unfinished black. Could I spray paint it (sand, black spraypaint, clearcoat)? I don't really want to pay a pro to paint it. That would double the cost of my cheap mod.
Yes. I have the same (similar PU) lip from fastwrx. I just lightly sanded it and used flat black Krylon Fusion. No clear coat. It's held up to snow and rain so far. I expect it won't bleach in the sun as badly as the bare PU also.
What about mounting? It came with screws and glue. Is there a good type of double sided tape to use too?
3M thin automotive double sided tape always works... but you shouldn't need it. I just drilled new holes in my bumper and used tiny nuts/bolts to close any gaps. My thinking was that tape would be a pain if you plan to take it off in the winter or anytime you need to drive up ramps. How may screws did it come with? I know the 04/05 bumper doesn't have quite the underlip that the 06/07 does, so I can see why you'd be concerned.
Typically, an auto body shop uses a special chemical that basically softens the PU so paint can adhere. But you can buy a dozen cans of Krylon for what youd pay to have painted the real way.