Exploration is by far the "grindiest" way to make many credits.
I'll agree that a better GalMap would be nice, but I don't see how a boycott could bring FDev to prioritize the GalMap.
For the part why the pay for the same data over and over again: Probably for confirmation reasons. In science for example you don't rely on a single result, you repeat the experiment (if possible) hundred or thousand times to make sure your results are correct. Maybe UC has the same politics? Though it's still not a reason to pay the full payout for the 10000th scan of a ELW. Should be reduced with everytime the planet is scanned. I personally like to imagine how my chara sits for weeks on some spacestations, haggling with some UC representative for hours about the price of Level 3 scans of ELWs and WWs.
Exploration, like so many other things in this game, is unfinished and won't stay in this state for ever. I'm sure that reworks of the Galmap are on FDevs list, too. So maybe you should have patience instead of a boycott