Does alien tech scale with time in XCOM: Enemy Unknown?

If I forgo completing the Alien Base Assault mission for a few game months, will the aliens advance as well, making the mission harder?

I realize incidental missions get more difficult and scale, but does a story mission, like the Alien Base, change the longer I put it off?

Yes, it will get harder. I waited a few months on my first play through and was fighting cyberdiscs, cryssalids, and a few mutons.

On my second play through I went right away for the panic reduction and 2-3 cryssalids were the highest level enemy I fought.

Strategically if you can wait and use the assault to reduce panic when you need it, that would be useful.

Well, the enemy's tech does not improve BUT their soldiers get harder and harder. Like mutton to berserker to elite mutton.