Kris touched on this a little the other day in the comments about trying to decide how much pureed pumpkin to use in a recipe as a substitute for oil/butter in a batch of pumpkin bread. She suggested to try a little bit to start and see how the final product turned out. Then, the next time, use a bit more and see what the results are like.
This is exactly how I approach this sort of situation. If I'm just baby-stepping my way with a recipe, trying a small amount of the "new" ingredient, there's less chance it will turn out horrible and a greater chance we will still like the end result. My "usual" formula is to try using 1/4 of the new ingredient to use as a substitute.
This month when I was cleaning the baking cupboard, I came across a baggie of carob powder. I used to love carob, so when I saw it again I thought I'd enjoy it as a substitute in hot cocoa. for my own taste, it was too fruity and lacked the bitterness that I enjoy in cocoa powder. so the baggie just sat in the cupboard until I found it in my cabinetry excavations.
Yesterday, I was wanting to make some brownies, but we're very low on cocoa powder. Cocoa powder is not a necessity (I could hear several gasps through the internet just now), so it's not high on my grocery priority list. (The best price on cocoa powder is a 20-30 minute drive from my house. I'll pick some up when I'm down that way again.) Anyway, I wanted to make brownies, yet also wanted to spare some of the cocoa powder. Remembering the baggie of carob powder, I decided to substitute 1/4 of the called-for cocoa powder with carob. The brownies came out delicious and absolutely no one knew any different.
Trying just a little at a time is also a good strategy for using up less desirable foodstuffs. I occasionally will get this wild idea to buy a package of seaweed, even though I know I don't like the taste of the stuff. When I come across a lingering package of seaweed in the pantry, I use it up in tiny, tiny amounts added to something like tuna casserole, or chicken soup, or stir fry. The first time i will try a small square of the seaweed torn into tiny bits. The next time, I'll add a bit more, and so on, until it's just too flavorful for me.
Baby steps. I risk less while trying something new.
