Advice, this is a long one.

 The key is knowing where the tipping point is between the two.     

And there lies the problem. Getting enough knowledge to make an intelligent decision on how to deal with the tax situation in the best way. I doubt the tax situation is going to get any better, so it's up to me to stumble my way through as well as I can and grin and bare it.

It's an individual's decision, but one must cut their cloth according to their goals. Having to file a US tax return and a UK tax return is a complication most people in the world will not understand. Your goal may be to stay invested in the US, reap the largest financial rewards possible, and pay the least amount of tax possible to both countries (and all that entails). Or, your goal may be to keep it as simple as possible, but with the knowledge that you may pay more tax overall (usually to the UK) but relieving yourself from the stress of the balancing act; allowing you to enjoy your retirement in the UK.

It's not easy, but it will only be as difficult as you wish it to be. There is no one correct way for everyone in this situation. The 'epiphany' is the moment you determine your goal and what is important to you. Your aptitude for dealing with the potential complications will determine whether you employ a tax accountant, or you feel confident enough to self-file. A professional will always strive to make sure you pay the least amount of tax, both accurately and legally, today as well as planning for the future. By self-filing, you may pay more tax (or maybe not); but it may be offset by not having to pay professional fees. The key is knowing where the tipping point is between the two.     

Excellent post! The OP has already made one important decision, he just accepts that he'll be taxed in the UK on an arising basis. A professional advisor might try to avoid that, but the OP knows his intentions and it's exactly what I would do.