Ya, the bolster will work for level 55s as well, if they are under geared. Could you post the stats on what you are seeing on PTS for your guy wearing legacy gear (or send the information to CommunitySupport@swtor.com, subject: ATTN Rob Hinkle, if you don't want to dirty up the thread). It certainly is the intention that your 55 wearing level 35 gear should get bolstered back up. To give everyone an idea (and BIG caveat here, this number is still in flux), but currently I would expect the new 55 bolster to be getting people into gear right around (statistically) non-augmented EWH.
Here you go Rob.
Im in legacy gear with lvl 33 purples or less.
When I enter PVP, I get a 273EXP boost and AIM boost to 1289(+177) and END boost to 1210(+225)
While this might be recruit level, the issue with 30-54 and 55 brackets is that the EXP boost on gear in the current system will severely outpace this bolster as the removal of the DR and the lack of gear upgrades until 55 will produce a large gear gap in the 30-54. The 55 bracket will suffer as well since the Partisan gear has more EXP and other stats than even elite WH does, let alone the Conqueror gear. I know eventually EWH will get to 55, but the intital shock might be too much for lower level or new entries to PVP to bare.
I am not sure how you solve this besides increasing the EXP boost. I understand you don't want to trivialize PVP gear, but if you are not geared in the current system, 2.0 could reintroduce some of the same gear issues we have now, where a fresh 50, without decent PVE gear, feels like a punching bag.