No Trellum its far worse than that, seem to be able to grow just about anything from seed,

its just this Strelitzia thats been evading all my attempts so far

yes there are other ways to propagate them, but first need a plant in order to do it. Yes florists love them, not just for their beauty but also because they are expensive, and are always in great demand as a single bloom or in a bouquet as you mentioned.
Quite a lot of time has passed since last caring for a Wisteria, so may be a bit rusty on this one.
Wisterias are not plants that like too much TLC and are best owned by someone, who always carries a pair of secateurs with them and enjoys heavy pruning, as they grow like triffids
No its not hard to keep a Wisteria blooming year after year. The most common reason for a Wisteria not to produce flowers is, lack of or timid pruning - they like to be cut back real hard twice a year.
As I said, they don't like too much TLC, therefore giving them too much fertilizer or over-watering them can also stop them from blooming. Didn't give mine any fertilizer at all, and only watered it infrequently, if at all, yet it bloomed profusely every year

until its demise, in that year, of the storm - and ouch, that porch was costly.
Know you don't currently have much space, but as Gina suggested, Wisterias are used for bonsai, and beautiful they are too - maybe this is your answer, could give you lots of pleasure whilst waiting to grow a larger one