I have a design for a "PhotoPost Credit System" where people can purchase credits which can be used to access galleries, fullsize images or downloads. For example, you could purchase 10,000 credits for $x and then when you attempt to use a gallery that has a cost associated with it you are prompted if you want to "purchase" this using your credits; if you do, then you never have to pay to see that category again and can view it anytime. Same with photos, you buy a photo, you can access the fullsize image anytime you want. Need more storage space for uploads? xxx credits will give you an addition xmb of space. You get the picture.
The nice thing about using a credits system is that I can see this being easy to integrate with other systems, like say the vB3 Subscriptions where buying a subscription gives you xxx credits in the PhotoPost area as part of your upgrade.
It won't be in 5.1, but if there is enough interest it might be available soon.
Please do not PM me for support or sales questions. Thank you for your understanding.