Folks have been operating single screw vessels for over a hundred years without a bow thruster and amazingly enough, some still do today. It would be a serious mistake to buy a boat with a bow thruster or install one on a boat without ever learning to dock the boat without one, under ANY conditions.
Just like GPS, a chartplotter or a radar set, a bow thruster is an AID to safe boating, but should never be relied upon for your survival!
It may be tough learning how to handle your single-screw boat, but it is NOTHING compared to trying to drive or dock most twin screw vessels on one engine! Of course, the rationale that if one fails, you will have the other holds very true, unless it is fuel tank contamination problem.
But there is no bow thruster needed with a twin-screw vessel. You wanna look really sharp docking? After a little practice docking a twin screw boat, you'll look like a true professional every time, no matter the conditions, especially backing in. That's how well a twin screw boat handles.
You can do it nearly as well with a single screw vessel with enough practice, but there may come a day when you'll have to pick another dock or wait out the tide.
If fuel economy is of any concern, a single screw vessel is most probably designed for that. I don't think you will save an appreciable amount of fuel by running on one of two engines, but you will be stressing that one engine a lot more than you would with both running. That could necessitate more frequent overhauls, a not so inexpensive endeavor.
And let us not even mention TWICE the engine maintenance, another considerable expense. Oops sorry, it just slipped out.
Anyway, have fun on whichever boat you choose. That's what it's supposed to be about.