Does the $2k you write of cover 2 flights (2 upgrades) or would it be $2k for each upgraded ticket, hence $4k?
If its $2k for both, it gets you the points and guarantees that you "hit the ground running" off of these long-haul flights and hence you are more effective at work, can get to things straight away, I would think it justifiable. There are lots of companies and organizations who allow upgradeable tickets on long-haul for precisely this reason. On top of that, no matter how good your record upgrading as GL, the PL will increase your success rate. Thus, on second thought, spend the $2k, upgrade those 2 flights and keep your PL.