New editions can be a good thing for a game as they can
- implement rule tweaks to improve the gaming experience (streamlining, less fideliness, better integration of theme and mechanisms)
- rebalance the game to keep it interesting for as many players as possible
- reset the power creep
- generate some hype and generate sales for the game - which can be essential to keep the game in print in the long term.
But such a new edition is only a good thing if it doesn't render models/fleets worthless/unplayable - so it should not be a means to drive the sales of new models. I think GW has been guilty of this in the past.
Changes in between editions also should not be too drastic in order to prevent player base fragmentation (see Warhammer Fantasy -> Age of Sigmar / 9th Age; or D&D3.5 -> D&D4 / Pathfinder).
The alternative to new game editions could be a living rulebook model - like Fantasy Flight Games now uses for it's Living Card Games. The games don't ship anymore with a full rulebook, but just with the getting started rules, while the full rules can be found online on the FFG homepage. I can see the benefits of such a system, but I personally don't like it as it means that the players have no certainty that certain cards/strategies (= models/rules for a tabletop game) are still valid or have been errated since the last game. I very much prefer to have a complete gaming experience that I can rely on for a set period of time, followed by a new edition with a proper lead-time (with spoilers and community engagement).