The 'ripple effect' that concerns me most is what happens when all of the systems neighboring your homeworld are Mark III or Mark IV, especially if they happen to have something that attracts Special Forces intervention (which is possible, since I've seen Core Shield Generators spawn on worlds neighboring my homeworld before). Wearing that down will be a slog, even if you spent your first 13000 knowledge on fleet ships (or starships, but on one planet you don't really have the energy necessary for a sizable starship fleet). Granted, this isn't that likely on the more open map types, but on more constricted maps (X maps, mostly) I've run across games where not only were my one or two neighboring worlds were Mark III or Mark IV, but also all the worlds within two or three jumps of the homeworld were Mark III or higher. A Mark IV guardpost, if its Mark I version is to have roughly the firepower of a cap of Mark I fleet ships, is roughly as powerful as my entire Mark I fleet. When you throw in the defending ships, it starts looking like a game you don't really have a chance at winning.
Currently, if you start out with only Mark IV worlds as neighbors, the early game is more difficult than normal. If the guardposts get the kind of buff being considered here, where a single Mark I guardpost is equivalent to a cap of Mark I fleet ships, it starts to look like breaking out of your homeworld if you get that kind of starting position is almost impossible.
I don't mind seeing guardposts buffed, but I think making each post the firepower equivalent of a cap of same-mark fleet ships is too much. I'd sooner see them all brought in line in terms of firepower to the current MLRS and see how things are after that.