Well, better too many ideas than not enough! The more great ideas you have that we want to see, the more money you will make of those ideas, so both sides profit from it.
The problem is that all the great new stuff you come up with and can't/won't leave out delays you
that long, that we won't be able to see even 10% of them all. Of course this is very frustrating, to know the many awesome things you still have in store and want to "get out there", but just not the time to do it. I guess almost all of your potential customers and fans would prefer to see "just" your initial great ideas, but 100% of them every few months or so, than 10% of even more great ideas every few years...it's no use for either of us if you don't finish a book in a reasonable amount of time, you won't be able to show all the new things you came up with and we won't be able to see them because we will all die of old age before even half of them are done
I'm not saying just ignore these ideas completely. How about this: Once the snowballs start flying, why don't you write down this new idea in a few short sentences, take a step back (not literally) and think for a minute if this is something you really need to include in your planned 32 page book. If the answer is no (you have a great idea about a paragon level vampire that doesn't fit into the heroic tier section of the bestiary books), you leave it be for the time being. Don't start fleshing out the idea or even write a quick stat block for it. I'm sure once the time comes for the second book and you look at your notes, the more detailed ideas will come back.
Honestly, I have no idea if such an approach would work at all, but when I hear that the next three or four books are already 20% completed, I can not help but think that you have actually been working on them for several hours already.
Anyway, just throwing ideas around in the hope you will be able to focus a bit more on the current book which in the end will help all of us
