Whilst I don't have the 735xt I do have the Forerunner 245. Yes it was the baby one at the time.
I do know several people that have the 6 and other derivatives with the solar charging. And in all their experiences they would say that it doesn't add anything for them in real world use. The solar charger is just a topper upper and not something that can be compared to a true solar powered watch.
Keep in mind that you do lose some screen space with the solar ring.
Ultimately if you are happy with the price premium then go for it and enjoy. I will probably upgrade mine to a fenix at some point as I do enjoy using the watch as intended.