To the best of my knowledge, no, TNG hasn't been remastered. But recently (as you can see in another thread in this forum) I've been rewatching TNG and I've noticed what seems to be an improvement in visual quality. Mind you I'm watching these on dvd through on upgrading dvd player onto a 32" Samsung LCD television, so I think I'm simply seeing detail, clarity and even hearing new sounds that weren't coming through when I saw these original twenty years ago on a CRT television.
In regard to the existing f/x I find some of them cartoony, but I ascribe that more to poor choice in how some of them were executed. The visible tractor beams and such look ridiculously overdone and very cartoony. Some space scenes and f/x look more like they belong in 2D cel animation. Some of the colour saturation in the f/x is too much and looks like it should be toned down.
That said on the flip side the uniform colours seem to be coming off better. Too often in the past I thought the command uniforms looked rather mauve than red and the science uniforms looked more teal than blue.