I have noticed that over the years with more and more diving, drymouth is much less of a concern. One thing may be that I tryto begin 'over' hydrating myself the night before. I will drink a lot of water beofore bed even if I have to get up in the middle of the night. First thing in the morning, 32 oz. water.
Also, in about 1992, I decided that there is so much unknown about the effects of alcohol and diving, that I would set a minimum of 24 hours before and after diving to not drink any alcohol. We all know that alcohol dehydrates us, so I thought why fight that battle also. If I'm going on a trip where I will be diving over several days, I extend the pre-dive ban to 36 hours and no alcohol for the duration of the trip.
Trust me, it's not always easy as I love my Guinness!
I now dive an Aqualung Legend LX and have spent up to 90 minutes under water on one dive. Every so often I take the reg out, build up a mouthful of spit and swallow.
I find the dry mouth at the end of a long dive to be annoying at most, but nothing I would buy a bio-filter for. Pre hydration, no alcohol work just fine and actually saves money!