In Holland I have seen relatively cheap (approx. 200 Euro) 4-stroke generators.
If you buy a generator, buy at least a 4-stroke. The noise is much less, and the smell of two-stroke is horrible, not to mention the pollution.
Also two-stroke engines run at higher revs., because of this noise levels increase rapidly when the generator ages.
The Honda's are beautiful, the luxury models have electronic output regulation (inverter techology), so they will provide you with 'clean' electricity. However there is a price to pay (> 800 euro).
If you will use it very often, then the Honda-class is the only one to consider. If not I'd go for a inexpensive 4-stroke.
To the floating earth, nice story, but per definition every generator has a floating earth unless you connect it to earthing plate dug into the big sphere under your feet (or in water). That still would not help a great deal unless you would also introduce a safety switch reacting on 'leak-currents'
I've only just noticed that you have a Centaur - I had a Centaur until we upgraded to a Nauticat 42 this summer, for a few years sabbatical and have been through the same thought process as you. I imagine that you are a member of the Westerly Owners' Association and the excellent Westerly yahoo list? You will get some good input from there, I imagine.
To your point - I wanted a generator because we had fridge, radar, extra lighting and a Mikuni heater all of which use a fair bit of power and we tended to use the boat in the winter. I finally came to the conclusion that there was no suitable place to stow a generator, if you are carrying a tender, oars and outboard. Before you buy, can I suggest that you mock up a box the size of your proposed generator and try cruising with that for a week before buying? It might pay to put bricks in to simulate the weight because it is very difficult to manoeveur heavy items into small spaces. Don't forget that you will also need to carry fuel maybe at a different oil ratio to your outboard.
I kept a small 350W inverter mainly for charging mobiles, etc. and relied on the engine (with upgraded alternator and Sterling smart charger) plus proper marine (Sterling) mains battery charger. That worked for us though I would have loved to have had space for a genny all the same as we do enjoy our comforts.
I do have to agree with you regarding size being a problem. Although the Centaur has storage space a plenty access is not easy. Even my tool box is too big to get in to a locker and will have to be changed.
In all honesty I don't expect to be using the genny alot. Mainly over the winter whilst I continue the refit. Part of the work invloves a new electrical system and will include a good shore power unit.
Having had many a useful reply I am probably going to opt for the cheaper 2 stroke genny.
Even if I find I can't keep it on board after the winter it will have served its purpose.
i did wonder if there is a way of creating a storage place fore it in the engine bay. perhaps by constructing a removable shelf over the drive shaft. of course I'll have to think about any risks due to the petrol left in it being close to the engine.