Hi Keith
Let's just look at it in perspective.
Both boats are beginning to get too large to trailer anyway so they will be water bound.
Hourly running costs, maintenance and moorings will be a little bit more, but in the grand scheme of things "very" little more.
The bigger boat will be a little less agile (assuming the same style of drive system and similar power to weight ratios), but that will be compensated by the more sure footedness whilst at speed on the water.
The only real downside I can see, and this is a fairly big one, based on an assumption (rather than knowledge) of the boat.
The Flyer made a great 17 foot starter boat. Easy to launch, rag around and bang back on it's trailer. The 23 should in theory simply be a much bigger and more stable version. This would assume that the dimensions have been stretched relative to the 17 footer (ie: whatever % the extra 6 feet in length gave was then applied to the beam).
Now the smaller Flyers are known for slamming. If the 24 is truly one foot wider than the 23 then that is a massive growth in beam compared to the growth in length. I can only see that his extra and non relative growth in beam is giong to enhance the slamming problem by a considerable margin.
In addition, this extra beam, "may" make the boat begin to exhibit some awkward handling characteristics at lower speeds (acting a bit like a hover craft in turns and carrying on sideways etc...).
Just some thoughts, although I'd love to know the real facts rather than my guesses so anyone who has had both please jump in...