I don't think so, but opinions vary. The first 6 do make some stabs at long-term arcs, but they're all pretty lame. For instance, the TNG crew does the best it can in an awkward situation in the first pair, and for some reason that's enough for the ship to be put on the Admiralty shit-list for like a year. Like their prior legendary adventures wouldn't have been enough to give them the benefit of the doubt?
In the first pair, Data also removes his emotion chip and Wesley appears for the first time in a while; in the third pair, you find out why Riker's dad wasn't at the wedding in Nemesis. And while that sounds like the sort of thing I'd really like - filling in continuity gaps like that is one of my favorite things in TrekLit, really - the stories there were worse than I'd have come up with if I'd had to just make my best guess.
Opinions do vary, but even the people that like them tend to view the second pair as the best, and that's the pair that stands alone the most, that contains no gap filling or continuity of note.
Mostly, I feel like the interconnected TrekLit universe is of an unusually high average quality - books are genuinely impressive in some way most of the time. They aren't just "here's a thing that could've happened next"; they're ambitious and meaningful and surprising and powerful. And the last three A Time To... books fit into that kind of high-stakes, taking-chances, interconnected quality brilliantly. The first 6 feel like they're still playing the standalone-numbered-novels game; stories that feel right, that remind you of your favorite characters, that don't surprise you or tell you anything new.
And since nothing later on really refers to the first six A Time To... novels anyway, for my money you're better off jumping in when the getting gets good.