About "Unique upgrades"... You can't use it for more than one race. They are built specially for the track. Just look on which tracks you can get them... Monako, Spa, Monza, Suzuka... Extremely low donwforce, or extremly high downforce. These tracks need special packets to improve speed of car, and team is giving you some special upgrades ONLY FOR THIS ONE TRACK.
If you are interested about real F1, then you will know that, real teams are doing the same. The worst, HRT, had special upgrade for Monako.
And why team is not using it longer? For the same reason, that you aren't using 11/9 wings on Monza (crap). Some tracks need more downforce, some tracks not. The other reason is that, team want to give you more downforce without wings adjustment. That's why u can drive fast sector 2 on Spa with 1/1 wings.