I used to scoff at people that suggested putting a thruster on their boat. "Just come in quicker... practce your docking... use prop walk to you advantage..."
Well, that is all fine and dandy as long as you are in a marina where you have enough room. However, I will warn you that many of the marinas in high rent districts (SWest Florida for example) are VERY, VERY, VERY, VERY TIGHT!!
One of the marinas we were at did not even have 40 feet on the fairway (between the oppisite side slips). Now, you do the math: if your boat is over 40 feet long, and you do not have 40 feet between you and the slip behind you, how would you like to get a single screw boat in there????? Now add in opposing tides and winds and other boats sticking out more than their slip is long, and you have a really serious docking problem. The only way you are getting out/in of that slip (and this is assuming a nice calm day) is with a whole lot of help on the dock and off. That is no fun, and since I like to singlehand, it is a serious pain.
I do not have a thruster and I am pretty darned good at getting a boat in/out of a slip... However, I would not have a problem putting one on my boat. If you need it to get out and sail more: GO BUY IT!! Put it on!! It is your money!! I find it unlikely that there is anyone that has a bow thruster that would say, "Man I wish I would never have put that thing on!!"
And when you come into your slip and do your perfect push button parking, you can laugh at all of the other guys breaking feet and patching gellcoat!! HAHA!!!