Is a new HVAC system worth it?

Here is what I would look at if it were me. This is save money.

You have an R-22 System now. And im sure as you know you can not put and R-410A in with out replacing everything.

Plan B. They are selling current production R-22 Units. They are calling them R-22 Dry units.

In a nushell to skate around the EPA R-22 deal. They ship with nitrogen from the factory. Then the tech field installs the refrigerant R-22 in to the unit. So all you have to do is just replace the ouside unit. Simple swap out. And yes the new unit will be a 13 Seer R-22 unit it will work just fine on a 10 Seer indoor coil. I do them all day long. On an 11 year old system if no know leaks were known I would do a swap out. If you had a burn out your going to have to acid test and flush line set if needed. The units if you know someone can get it for you around 1000 bucks. If not figure installed around 2800-3000 bucks. The replacement R-22 unit would need roughly 9lbs or R-22 with 25 ft of line set.

BTW not to bore you with knowledge here. But the R-22 units are the same thing as a R410-A unit (which is current federal mandate for refrigerant) What they simply do at the factory is put mineral oil in the compressor so it can run only on R-22. The compressor does not care what gas is it in it. So long as the correct oil is in the compressor in relation to the gas. (and for you nit pickers yes it not GAS its refrigerant) In R410A its runs at much higher pressures than R-22 so thats why they tell you you can not re-use an R-22 evaporator coil. R410A outside has to match the inside.

All equipment breaks eventually. Lennox makes a fine product and you should be happy with that combination of furnace/AC. The 98.2% AFUE and Seer rating of 21 should save you significantly on energy costs over your old equipment.