I'm surprised that no one has mentioned polypropylene baselayer pants/tights yet. Except for the real crappy abrasion resistance (lack thereof), it would be great material for this purpose. Super hydrophobic, high thermal resistance, and relatively low cost.
Another downside is stink buildup, but if one wears some merino or linen underwear beneath, should be much less of an issue.
I haven't tried them yet myself, but i theoretically like the idea of leg warmers more than full on tights. I once had a chronic jock itch infection that was very hard to get rid of and am a bit paranoid about ever having that develop again, so i like to keep that area as cool and dry as possible. Leg warmers would be much better in that regard.
Anyways, i've done the tights thing and most often with my tyvek rain kilt. Looks probably pretty funny and "un-masculine" but found it works good. It has to be fairly cold and/or cold wet for me to go that route though. Tried silk weight powerdry and RAB Meco stuff. Have yet to try the polypro pants i picked up in AK.