There's no particular benefit to using 50 ohm coax instead of 75 ohm coax is the antenna system is set up to use 75 ohm coax to start with. If it's working with RG-59 cable then it would seem to be set up to do so. If you changed that to RG-58 then you'd also have to do some impedance matching changes, which doesn't have to be 'simple' at all. Typically, there's not enough difference in loss between those two cables to make any difference. I think I'd replace that RG-59 with RG-59 cable. As for the connectors, a good connector isn't going to make any noticeable difference. There are other brands of connectors that are much better than Radio Shack's, easier to deal with. Use what you got or have access to.
- 'Doc