My 2006 Nissan Altima is having problems...?

My 2006 Nissan Altima has about 105K miles and recently had a few problems that we fixed and started a couple new ones.

Last 2 problems fixed about 2 months ago:

- Passenger side engine mount replaced

- Thermostat and heater control valve replaced

About a week ago, few new problems:

- Cylinder #3 misfire (replaced plugs, but appears related to the next problem)

- Pressure test of cooling system indicates a leak into cylinder 3. Appears to be a head gasket, but guess I won't really know until removed and tested.

- AC having electrical issues on the compressor and loss of freon (or whatever gas is in it now).

Is this common for Altimas? I've heard from two mechanics (one that did the diagnosis, and another a few years ago) that Altimas have issues and they wouldn't recommend them. I've had multiple Nissan Sentras and one Altima. The Altima has definitely been giving me problems that I wouldn't have expected until 200K or more miles.

So opinion question, would you fix it if and if so, what would be the upper cost before looking to invest in a newer car? I don't really have a place to work on it myself, plus can't really afford to have the car out of use for that long (wife will not put up with having to drop/pick me up from work much longer).

Additional details: Couple rust spots, but nothing out of control (yet at least) and interior blower motor seems weak (not putting out a lot of air flow).