I don't know why it wouldn't be a good idea. After all, well developed vassals are stronger allies. If you keep their land safe from enemy invaders and don't lose your own territory (both are quite easy) they won't leave you. And I seldom request vassal tribute, because I often have resources to spare for trading, in case the AI has some resource I need. I don't give financial support mostly, but OB, world maps, extra resources and some of my lower-tier techs are my favorite presents and the vassal likes them too. I think the AI should think of OB with their master as a gift instead of a trade, as the master can traverse their territory anyway (international trade is a mutual benefir though).
This all comes down to pleased/friendly vassal AIs in the end, if it makes any difference.