One of the serious bakers will be able to give you a better answer, but I don't think you can ever really do a direct substitution for vanilla. Almond extract, for example, is a lot stronger and if you used equal amounts you could end up with something nearly inedible.
I've had some luck with one or two recipes significantly reducing the amount vanilla, so there's just enough for that subtle richness, and then using a couple drops of almond or a few tablespoons of a liqueur or something like that.