I've had a coupla brews where I've slightly caramellised the dextrose dissolving it over too hot &/or for too long......it gave a good result adding to the malty richness of the taste. I think it could be overdone and get into a sickly-sweet. I'm assuming that once caramellised the sugar is less fermentable so it might be a case of needing to add extra fermentables to maintain alc/vol levels, and also added hopping to balance sweetness.
(I was going for a higher alc/vol- 8-9% hence a lot of dextrose takin a long time to dissolve and it got caramellised )
cheers!