John Mullins describes a lightweight technique called the "long interview" in The New Business Road Test. I've only used this seriously once. The results of my trial provided good insights but were not as definite as I'd hoped.
Another method I heard from a startup marketing guru is that if you have a large number of users running a free or pre-release version, you should ask them, "how disappointed would you be if this product were discontinued?" You have product-market fit when a significant portion answer that they would be "very disappointed."
I've also had the impression that feature requests are not a particularly useful metric by themselves. The fact that you have conflicting feature requests probably indicates that your market is highly subsegmented. It might be useful to try to map these subsegments demographically and need-wise.