Bottomline - I think H-1 should be renewed.
A little more info: A few months ago, I used to feel strongly that AOS applicants should keep their H-1 active for several reasons. Two of these are:
One, EAD issuance was erratic and CIS had discontinued issuance of interim EAD's (that is, if in 90 days your EAD is not issued, you could walk with a infopass appointment to your local CIS office and get an EAD). Thus, EAD's were unreliable and given for only a year. You could have interruptions in your work.
Two, if your AOS were to be denied (even in error), you would have no way to work, because the EAD goes with the AOS. And since there is no appeal against AOS denial, only an MTR can be filed. While the MTR is pending, you are not given a work authorization (as of now, July 2008). In addition, you would not be able to get n H-1 extension beyond the original six years because nothing is pending and "final action" has been taken on your green card. This could result in a situation that can be very dangerous. You do not have an H-1, a pending MTR gives you no legal status to sty in the US. Not only can you not work, you are deportable and you are accruing illegal presence even though the MTR is pending.
While CIS has done well to eliminate the first concern by reinstating the interim EAD issuance policy, the second concern still bothers me. While erroneous denials are few an far between (thank heavens), they do, nevertheless, occur. So, just maintain your peace of mind by keeping your H-1 active. That is my opinion. Reasonable people can easily argue against this and perhaps, their points of view may be just as valid.
All the above holds true, whether or not you intend to use AC21 portability.