Yes provided you a) know what you are buying b) remember the sticker prices in the US are before tax so you need to add the local sales taxes etc to it for the comparable price and c) can get it back without paying tax and duty.
On a) you need a good idea of what spec at what price in the UK to know whether its a bargain or not. Some bikes carry the same name on each side of the Atlantic but are quite different spec bikes of completely different values.
On b) it varies state by state and can be zero in some states. So don't just walk into a New York bike shop and buy one. Do some homework in case you are going somewhere with zero sales tax but don't go somewhere where you'll need to fly back because most airlines charge quite a bit now for a bike. But if you are driving up to Vermont for the weekend.....
On c) you will have to pay duty and VAT amounting in total to about 37% of the purchase price IIRC unless you:
- have had your normal home outside the EC for a continuous period of at least 12 months
- have possessed and used the goods for at least 6 months outside the EC before they are imported
It sounds like you are going to fall foul of this which means you are either going to hope to take it through the nothing to declare channel and get away with it or pay up. Remember its up to you to prove you qualify for tax and duty free not them to prove you don't if they stop you. This part can completely screw up the economics of importing one.
Don't underestimate Customs. I have brought a few bikes back over the years and always declared them. As a result I've had some interesting chats with them. One is they do know their bikes and have a big book with all the bikes and values in it (at least at Heathrow they did), second is people forget the customs officers do this day in day out and have seen every trick and excuse in the book so if you do get stopped come clean straight away as the longer you try your amateur denials the more likely they are to confiscate the bike and/or add heavy penalties charges