Gold plating helps a lot. I've been testing this recently, without the gold plating, the HASL finish quickly oxidises and you get resistance readings upto and exceeding 600ohm. You also need to press much harder.
Also, the membranes start to become a bit crap and don't conduct aswell. Cleaning them with some alcohol/ roughing them up helps a bit... buttt... I have a new magic solution to make all your problems go away!
Save yourself a ton of money buying gold ENIG board and buy yourself some of these little beauties. Thank me later.
They'll work with your HASL boards a treat, immediate conductivity. Seem to be very strong, hard wearing and stick like poop to a blanket.