The so called " speed arms race" only exists because currently the game exists as nothing but a lot of assassins. Even the generals are, in large, played as assassins. When the kinks are worked out and competitive play emerges then a more team focused strategy will take the lead. Until teams quit competing for the right to claim most kills and simply focus on winning, IE: having heroes that push as well as complimentary assassins / protectors, then its going to be a race for speed because everyone is focused on the kills.
Example: I guarantee if you put me and two buddies in a match, two of us will play assassins as assassins, one of us will play someone with the sole purpose of pushing. That pusher in no way needs boots. Hes never going to need to run away because he's got teamates that cover him and take care of the assassinations. The only movement he needs is a teleport to base and back for upping citadel and buying his start items + consumables. Even my two assassins aren't going to try and whore out every +speed gear there is, because they play smart. Theyre going to let you come into our defenses far enough that a partner can port in behind or come in from a lane behind (such as the middle 2 horizontal lanes on levithian) and cut you off. Or theyre going to make sure and whittle, whittle, burst; they wont give you the chance to try and escape, thus negating the boots. And hey, even if you get away- OH WELL. Theyve still accomplished a couple things: moved you from your lane so we can push it, cost you experience by removing you from your lane, and removing a potential threat from our pushing player. In fact, some quick math shows that the kill is actually quicker for you to return to combat (in some maps):
Die: ~30 seconds of penalty
Escape: either time to walk or port to base. If you port to base you either walk back or wait 30 seconds for the port cooldown.
Bottom line: speed items or there functionality isnt an issue in my opinion, its easy enough to counter through survivability, more offense, or simple avoidance through playing more defensive. It costs the player way too much, not in gold really, but in the opportunities missed by using those item slots for speed instead of something else.