Your 50hp four stroke is a nice engine (a Suzuki in disguise) - the only 60hp 2 stroke I would swap it for would be an Etec (but I'd go up to a 75 Etec) as it would give you an improvement in economy - other than that I think the downsides of the 60hp you're suggesting (more noise, rougher running at idle/trolling speeds, higher fuel use) wouldn't outweigh the only upside of slightly more power.
I look after the shetland owners club for scotland and there is no way on earth I would swap a 50hp 4 stroke for a 2 stroke unless the 2 stroke was worth a lot more than my 4 stroke and in that case I would sell it and get a better 4 stroke!
I would also not buy an engine from a manufacture who closed there uk office and did not exhibit at the UK largest boat show last year and who's closest dealer is over 250 miles away and who's market share is shrinking! i.e the etec.
last but not least. the 50hp is more than enough for that boat and it will be a very rare day that you can will have the throttle wide open and even more so due to where you live.
Save your time and money and stick with what you have.