I think the "donate and get features" model is viable and interesting.
Vitals features (like the payout history) should not be in that model. It needs to be free. I believe you make all the efforts to make this pool secure, but I like to verify by myself that everything is ok. Everything that concern transactions between us (the miners) and you (the pool) should be available for both sides. Like that, both sides can be sure they trade correctly.
One thing I would really be willing to pay for is stats, a lot of them. How much Bitcoins by day, hour, minutes? In relation to the GHash of the pools? Complete network power in real-time? My percentage of the total network? Future projections of how much I will make for the next two weeks? How many Bitcoins I make at that MHash rate at this difficulty?
You, as the pool, have access to a lot of raw data. If you can sort this data, and offer an access to a well-presented page of stats, you have a little gold mine here.
Having to pay for mining on a pool is retarded. I don't see why I need to pay somebody so he can see all my informations about mining while I can mine by myself. A pool process and transfer data so, you should see yourself as a data-processing company. And what a data-processing company do? They sell their data, with nice little charts, predictions, hard facts and whatever you can think of.
Here's how I see that:
Basic account - You mine with all the features needed for mining and for security of the transaction between the pool and the miner.
Stats account - You can access a vast quantity of data. You have all the popular statistics functions, with a bunch more added to it.
Cost: It depends on what you offer. You don't want to have a high price for low value, because nobody will take. Let's 1% for example.
Stats-junkie account - You have everything. A wet dream of statisticians. Sort of account where you can sort anything by anything, and even where you can access the "coming soon" features, where you can try them.
Cost: As always, it depends on what you offer. For the example, let's say you charge 3%. Like I said, it is an ultimate wet dream, for an ultimate price.
Even more, you could sell this to people who don't mine at ABCPool, but would be interested in seeing that data. For those guys, you ask for more, because they don't mine for you. You charge something like 20$/month to have an access to all those stats, with API, email, SMS, whatever they need of. If you do that, be sure that you put a ceiling on the price for the miners, so the big big big miners don't pay more than those who only buy data.
You're not a pool, you are a data-processing business.