It looks like you are unable to roll Need on tokens if you own the tier as a higher item level, even if you are missing the LFR transmog.
If I am not able to collect the LFR transmog this way, then there is no reason for higher item level characters to run LFR.
I would have expected to be able to roll on these tokens since I am missing the transmog.
Correct.
This was explicitly documented in the 10.0.5 patch notes.
Fixed an issue where players could unconditionally roll Need on Set Tokens. The system will now check if the player owns the Token or the Set Piece itself at equal or greater power.
sadly this “fix” make the only way to get the full set for transmog is with the catalyst(or lucky raid farm) but since it have limited charges we need 2 characters of the same class 
Well that is a bummer. I guess there is even less reason for geared players to do LFR.
Blibli… Like in raid finder the Monk tier set is the best… At least, could we unlock the raid finder tier if we have a higher tier… or through renown… ? It’s like we can’t have it ?
Catalyze veteran gear for lfr appearances. If you wait until season 3, it will be free to catalyze.
If you dispose of it now (say, vend it), you can Item Restore to get it back in Season 3 and catalyze it for free to get the appropriate tier appearance.
But you won’t be able to upgrade item level after restoring (assuming S2 precedent holds; no crests from previous season), so if you want to have higher raid level tier appearances, you’ll have to upgrade them to the desired ilevel before banking or selling them. Kind of tough, sucking on crests you may need for actual gear, but that’s how it is for now.
Assuming there’ll be catch up gear similar to Siren Isle, you can pre-purchase items to catalyst for free post season. You can even buy a second set and upgrade it to champ for the normal mog.
I certainly did that with Season 1 LFR tier (Siren Isle shopping + free catalyst) but you have to have the upgrades ilevel track items somehow before the new season starts. Void Storage (remember that?) or bank slots would work, but if you didn’t remember to do that, the Item Restore is a good emergency fallback.
I completed all of TWW s1 Normal and all but one piece of Heroic and Mythic using item restore.