Ok this sort of sounds like a stupid thing, but I think Ancestor Worship and numen in general is underused in game because the only players who can actually see progress are full tradition. I think this should be changed slightly, so that full change people have minimal growth of numen during sacrifices. This should of course be minimal (like 1 point each time), but I think even the most minimal growth is superior to having 0 growth on a majorty of sacrificial acts.
The reason for this, is without being able to see any sort of growth (and at full change you rarely see even a single point increase in numen), players decide it's not worth their time. That's sad for one of the more unique aspects of the game, to be so unused.
Now I don't want to unbalance anything; full tradition needs the obvious advantage of numen, as that's really the only incentive tradition belief styles have.
So I think just scaling up the cost, but also the growth of numen generation, would solve this. It would still make it that full change takes absurdly long time to grow in numen, but it allows full change to see the progress, even if it's near-prohibitively costly to do so. Just being able to see the growth might be enough incentive for people to try it out a little bit, perhaps even enough to try switching down closer to tradition or neutral. Scaled correctly, full tradition players wouldn't see any difference, either. Basically it would still make full change players at a major disadvantage -- which they should be at -- but again, allow them to atleast notice some, albeit minimal, progress.
But as the game is, unless you play a specific way (I.E. purely ancestral based; which is usually used for nefarious purposes), there is no incentive to be traditional or use ancestor worship.
Other things for Ancestor Worship, I think there needs to be more religious structures; maybe burials where if you have an ancestor buried there you get a numen bonus. Or even just static shrines, which work like the furniture shrine, but can be used by anyone. This would be good for a roleplay aspect, as sometimes there are just pretty areas in game that a shrine might feel right in; but as shrines work, nobody can use a shrine there without having a bunch of portable wooden shrines all over for each individual pilgrim.