We were in a similar situation where combats were far too easy because there was just one per day and everyone would go hog wild with their Daily powers. To combat this I would recommend instituting a house rule that an extended rest cannot be taken until after three milestones have been reached. That way you can have only one encounter in the session that is more moderate and won't take up 3/4 of your time, so you can spend the rest of the time on social encounters. And because of the houserule it won't be a cakewalk from Daily spamming.
Also there is nothing in the rules that assumes 1 session = 1 extended rest. this is a way a lot of groups run, but it does cause these sorts of problems.
An extended rest should occur when the DM says it does, even if that is over multiples sessions/in game days.