Coredump, I think that your credit idea is a little too confusing in practice. Keeping a degree of standardization regarding the amount of rewards that each adventure is worth will reduce the potential for abuse by min/max when you cash in your credit.
My suggestion is a bit more consistent and futureproof. Assume that X, Y, and Z are equal to the rewards for a 4 hour adventure of Tiers 1, 2, and 3, respectively. The table would then look something like this
T1 2 hours = X/2
T1 4 hours = X
T1 8 hours = X*2
T2 2 hours = Y/2
T2 4 hours = Y
T2 8 hours = Y*2
T3 2 hours = Z/2
T3 4 hours = Z
T3 8 hours = Z*2
The only adventures that would need a separate reward calculated are the X-1 5-part modules and the individual parts of hardcover and Launch Event adventures.
By putting it all in the ALPG, you end up accomplishing two things. First, you've made it easier for DMs to calculate their total DM rewards by putting it all in a central location. Second, you're now forcing DMs to refer to the ALPG more often, which will subconsciously make them more familiar with its contents. If I have to continuously pass by the starting lifestyle table and the FAQ before reaching the DM rewards table; I'm more likely to retain that info, thus enabling me to recall it without having to look it up.