I think you are really underselling the advantage that fighting on your own planets gives you... If an exo intended to be a reasonable but not excessive challenge can't be beaten with a significant net gain of metal on your part then you're already going to lose.
I'm speaking from experience of having this exact scenario happen to me in multiple games in Classic. I would rebuild my entire fleet, only to have an exo a few minutes away (20 being an arbitrary value), too close to want to risk a significant portion of my fleet trying to attack a new planet or whatever. When I finished mopping up that exo, I'd need to rebuild the fleet again. Repeat, repeat, repeat.
I would not want to bring the exo to my doorstep early for any amount of metal. The cost exchange is not worth it:
1) By pulling the next exo in early,
every subsequent exo is moved up too (high cost) because exos aren't on a timer, but rather a budget. Zero out the line item early and it starts refilling immediately
2) The metal I gain from salvage is metal I would have gained anyway (no benefit)
3) The free metal I get in exchange for clicking this button--assuming it doesn't overflow my storage cap (risk!)--needs to be a significant percentage of my refleet costs (or no benefit)
Refleet costs are
massive. Its not a million metal. A million metal is the down payment in classic. You could
store 2 million easily enough, but refleeting? You'd burn through those reserves in ten or fifteen minutes....the remaining cost paid over the next
two hours.
The current conversion rate of Salvage to metal is too low. I believe that the salvage generated by any wave (including Exogalactic fleets) should provide 50-100% of the metal cost of what they destroy.
Its too low and too slow.
Chris talked about it the idea in his Chess analogy, but effectively, if you are able to fend off the fleet, you should come out of the experience with everything at ~100% and ready to go for the next round.
Should, but you don't. You never have. And the reasoning has always been as a balance counter to various super units. Never mind the fact that you'd get botgolem exowaves before you ever actually OWNED the bugger. There may be a reason I played with AIP-golems.