It is complicated. I had to build a complex model of my retirement that has a rough tax calculation built into it to see that by emphasizing Roth conversions between ER at 56 and age 70 that I would spend much less time in the 25% bracket once SS and RMDs begin and that the tax savings between 25% and 15% were much more than the value of the subsidies.
Others doing this "what-if" exercise should do a sensitivity analysis of sorts and look at the ramifications of excursions from the assumed investment return rate. Assuming the ACA subsidies are taken and opportunities for a ROTH conversion are reduced, then--
-- If investment returns are
worse than expected:
--- Less time/zero time in the 25% bracket, and it happens later in life.
--- Having the extra $$ in the portfolio (from taking the subsidies and spending less on health insurance, leaving money to grow) could be a very welcome cushion.
-- If investment returns are
better than expected:
-- More time in the 25% bracket (so paying higher absolute dollar amount in taxes), but the portfolio must be so much larger than originally predicted that overall withdrawals are still higher than if the original return rate had materialized. You're "winning the game", have an improved likelihood that your nest egg will see you to the end of your life, and the fact that you opted for the ACA subsidies early on and it eventually proved to be the less-than-optimum approach from a tax perspective makes no material difference to you whatsoever.
This way of thinking only applies to those who don't have significant needs to leave money behind.
IMO, guilt about qualifying for the subsidies is misplaced. It's not charity, its just a tax law and the money comes from general revenues. Not taking the subsidy would be just like sending an "extra" check to the Treasury for their use. In fact, some people are using the subsidy payments as a measure of merit for the ACA, so taking the subsidy helps them show that the program is "working."
“Anyone may arrange his affairs so that his taxes shall be as low as possible; he is not bound to choose that pattern which best pays the treasury. There is not even a patriotic duty to increase one's taxes. Over and over again the Courts have said that there is nothing sinister in so arranging affairs as to keep taxes as low as possible. Everyone does it, rich and poor alike and all do right, for nobody owes any public duty to pay more than the law demands.” - Judge Learned Hand