I'll take the models first, for a few reasons, one is they are cheaper in most cases, better designed, about as sturdy as some of the newer toys, you can customize them anyway you want and theres no risk in it loosing face value as a "collectors items" down the road.
As for the Toys, most of these are considered Collectors items and should be left on display only or still in its box. Not played with. The moment you try to customize a toy, there goes its value. (((( However if you never plan selling your toys, disregard this notion )))) With the model kits, knock yourself out!! Even though it takes a long time for you to build a model and paint it, etc. Theres a big sense of satisfaction when your done.
Plus if it should break, its a model and a little glue never hurt anyone. Big difference when a $200.00+ toy needs to be super glued!!