If the 55T fits your 110bcd then it should work. You can hunt down some spacers and use normal chainring bolts to run it without the little ring but like you said that requires spending more. Check that the chain isn't too tight in the gears you're likely to run.
yep shimano 4 bolt is now compatible with all shimano 4 bolt chainrings so you can switch between 50 and 55t relatively easily, good point about the chain though!
If the 55T fits your 110bcd then it should work. You can hunt down some spacers and use normal chainring bolts to run it without the little ring but like you said that requires spending more. Check that the chain isn't too tight in the gears you're likely to run.