Creating a Subscription Service involving Google Maps API

I work for a small consulting firm with a variety of customers who all
wish to take advantage of the Google Maps API in their websites. While
I'm happy to have each of them pay me to write the code to integrate
their sites with Google Maps, I'd much rather create a centralized web
service for each of my customers to come to instead: it would ease the
pain of rolling out new features and lower their cost for development
and integration.

>From a technical standpoint, this is a no-brainer. I would arrange to
get separate keys for each customer so that Google (as well as my
company) could track for whom each request would be made for. I think
the real issue here is whether Google would be kosher with me creating
such a service. I've read and re-read the terms of service several
times and to me this sounds like a grey area. Is anyone here either
from Google or external to Google able to give me some clarity about
whether Google would have a problem with us creating such a service for
our customers? We wouldn't be violating any of the branding clauses of
the Terms, but we would either be charging a subscription fee or a
per-request fee to our customers, or perhaps both.

Any information that anyone would have on this would be great. I've
called Google directly on this but they don't know how to route my call
or to whom, so I'm kind of stuck.

Many thanks!

Andy

P.S. Alternatively, is there a "pay-for-play" option with Google Maps?