I think if you have to park outside that's even more of a reason to protect your finish as it's exposed to the elements on a regular basis.
I just had Cquarts Finest done and it came out great and I think for me it was worth the $. I also did Xpel on the front end for additional protection. If you want to Xpel the entire car you looking at $4K - $5K depending on where you live.
It cost me $895 for the Xpel (entire front bumper, headlights, mirrors and about 24" up the hood) and $850 for the Cquartz Finest (including the rims). They apply the Cquartz right over the Xpel.
From what my detailer told me the version you can apply yourself does not last as long as the dealer version. The warranty for CQ Finest is two years. My car is in a garage at home and at work so I was told it could last as long as five years if you apply Cquartz Reload twice a year. It's a spray that adds additional gloss and was made to enhance the ceramic coating.
I just applied it for the first time and it was a piece a cake, spray it on, wipe it off and buff a little. It gave additional pop to the shine. Took me 30 min to do the entire car.
If you don't want to spend that kind of money I'd put a good sealer on (Power Lock looks great and last a long time) then top off with a good quality wax. If you can do that twice a year you should good to go.
As far as a cover goes, unless the car is CLEAN when you put that cover on you will introduce scratches from just putting it on and off. It's a pain in the ass when it gets windy out as it will blow off even if you tie from underneath.