Thinking about joining Plusnet's upto 38meg fibre service and speed estimate is 22-32meg. I obviously want to get as far up that as possible and wondered if buying another router might do better for speed than the 'Hub One' supplied. Not really bothered about wifi range as I use homeplugs anyway. So would I just be wasting my money as far as speed goes?.
The real answer to your question is that no-one really knows the answer. If may work at the top end of the estimate or it may not. It's called an estimate for good reason
Not very helpful I know but nobody can give you a 100% guarantee. The Plusnet Hub One is the same as a BT Home Hub 5 Type A so should be more than able to handle 32Mbps download IF the line can deliver that in real life.
You may find that the homeplugs cause issues and slow you down (that's not that unusual). Again it is a try it and see.
Given the Hub One should only cost you the postage, it maybe worth while getting it and seeing if it works for you.