Like you, I have a strong preference for the single spey, whatever bank I am on.
For a period during the 80-s, I and some friends leased a beat in Norway that only was right bank. (Back then such a beat normallly was half the price of what the opponents on the left bank payed. Especially if the right one was steep and overgrown.)
One of us was lefthanded and had a distinct bonus. It was so frustrationg to see him in easy action that I decided to only fish left handed for a while. It was testing at first but after a few days it all worked out. Since I almost prefer the right bank, as the competition appears to be slightly less.
I agree with Kush, and others, that the ""backhand" solves meny situations - but it will never be more than a compromise to me.
In Underhand casts it actually is beneficial to have the strongest hand at the butt, as that cast relies on a push in the upper hand simultanious with an even stronger pull in the butt. For old dogs like me it is hard to get that right with the dominant hand uppermost - it still is used to when long and heavy lines had to be whacked out with brutal force......
My best advice is to practice the left hand casting. Do it at first in those right bank runs that best are covered with shorter casts - then one doesn't feel that any time really is lost.