@Marksfish
No, I don't think that you're being too simplistic.
Whether it's better to send Euros to TW, or to send GBP and let TW do the conversion, is another question. I'll probably do the latter because there's a bit less work involved.
Obviously, I would prefer to continue paying the direct debits from Starling. To that end, I'm still pursuing the utility companies and the ayuntamiento to make the necessary system changes for that to happen.
With some help from me, the management company that handles the affairs of my Comunidad de Propietarios has successfully updated its system, so I know that it is still possible for Spanish creditors to take payments from a UK bank account by SEPA direct debit.
Poco a poco ...