I don't think the problem is the small front wheel, its the tiny stem some models are spec'd with. Change it to a longer one and the twitchiness will vanish (I have done this on all my terrys). All my terrys have pretty neutral steering with a long enough stem (9-10 cm).
Some of us need the 24" front wheel if we have very long femurs but a short reach. For me, they handle way better than other stock bikes I have tried, although I am sure a custom Luna can be built to deal with these issues too.