Work less and make more, wouldn't that be the dream 😉 I smell a troll, maybe...if not, well, here goes.
1) If you're not a fan of hygiene checks, guess what 50% of ortho is about - checks!
2) Same for pedo - the only ortho cases I refer out are phase one.
3) With advancement of clear aligners, GPs are doing more and more ortho (see #2), which means you are stuck with more difficult cases and with less and less referrals. So, you'd have to wine/dine more GPs to get your piece of the pie. Now imagine you piss off a patient as a GP - you'd lose that patient and maybe 2-3 more of their family/friends. If you piss off a patient from a referral source, you are risking ALL of the patients from that referral source.
4) Becoming a specialist now would mean selling your practice (or getting a full-time associate) while you are in school for 2 years. This means a massive loss of revenue. I wouldn't put an associate for 2 years, as it would devaluate your practice, which you'd most likely have to sell upon graduation, anyway.
If you own your practice and have been there for more than 3 years, 250-300K is kinda low. Perhaps you need to optimize your practice instead to get you to the 400K? Have you incorporated ortho into your practice? Have you though about bringing in an associate to decrease your work load?