Nagging secondary air injection codes.
 

I've gone in deep twice on the wife's '02 Boxster trying to stop the P0410 and P1411 codes being thrown. The first time I pulled the right side intake and replaced the combination valve. The second time I pulled both intakes, cleaned them and checked all the vacuum lines. It's still throwing the same codes after about six driving sessions. Engine performance appears nominal. Reading live data on the Durametric reveals nothing that jumping out at me. Where do I go next?

If you search there is an ROW hack that deleted the air injection system w/o generating any codes. The air injection system was not fitted in Europe and it won't warm our side of the globe.
It has been discussed on this and other Boxster/911 Forums previously.

I replaced the Changeover and Cutoff valves on my 2000 and haven't seen the P0410 and P1411 codes since.

There is a procedure to check this system......All you really need is a hand vacuum pump and Durametric. ....
I've repaired numerous boxsters where the vacuum canister failed and wouldn't let the system pull enough vacuum to operate. ...

Also when the vacuum canister fails the adaption will usually be around +2% on both banks in idle range

Bell's suggestion is very good. I chased this issue for two years and it turned out it was the vacuum canister

Vacuum canister, excellent suggestion gentlemen! Looks like I'll have to dive in there again :(

If you have a hand pump just use long needle nose plyers ams pop it off the canister, put the hand pump right on it and see if it holds vacuum

I fought this battle too. I changed the Combo valve and the changeover switch. I also looked very closely at all the vacuum hoses. I ended up replacing most of the vacuum lines and especially the 'y' connectors (I have two, one 3 way and a 4 way) as vacuum lines were falling out of them easily. These code are gone but each time I fix one a new one rears it's head. Now fighting the 'expensive' one, P0430. I've changed O2 sensors but code still comes up. I'm having fits about the cost of new Cat's. I'm sorry a little off topic here. My original codes were fixed with new valves and vacuum lines. I did find an easier way to get at the Valves by the way. After some inspection I found I could remove the Valves and line by removing the Alternator and going in from the front of the engine, didn't need to remove the intake manifolds.

In theory you can delete all the SAI and still pass SMOG if you get an ROW reflash.
I raised this issue a few months ago but details are still pending:
Air pump removal-- weight reduction - 986 Forum - for Porsche Boxster Owners and Others
Suggest you google Boxster SAI ROW reflash. This is an appealing projectbut the devil is in the details of the SMoG test .I am sure you would pass the visual but am concerned a California type Smog test would flag the ROW reflash. Anyone tried it??