Re: Improving my cast
For the quickest improvements in your casting I would suggest getting lessons from a good casting instructor and following those up with practice. Books and video's can't see your casts but will make you a more well-rounded caster and may present points that you might not have considered.
I don't believe practicing casting without water hurts at all. You can do almost every cast on land that you can do on water. With weights or grass leaders you can even get a decent roll cast on dry ground.
The beauty of lessons is that you get instant feedback on your casts. This is the stuff you hopefully remember when reinforcing the lessons with practice.
Casting is casting, be it on the water or not on the water. When practicing at the park I start off with close, accuracy work, then tricky shots like curves, aerial mends and single-handed spey techniques and such and then distance mixed in with more accuracy. Every single one of these helps when I get on the water to fish. Part of what I really enjoy in fly fishing lately is going for the hard to reach fish.
I always have a rod in the car and manage to get out just casting 4-5 times a week if I'm not fishing. I'm not letting the lack of nearby water to cast on stop me from improving my game. Fly casting is an integral part of fly fishing and all else being equal the better caster will catch more fish for obvious reasons.
Just as some say they know people who cast well but can't catch fish I know many more people who can't cast well and their catch rate reflects that.