It's pointlessly subject to being extravagant (6)
I believe the answer is:
lavish
'extravagant' is the definition.
(synonyms)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for lavish that I've seen before include "Generous - liberal" , "Sumptuous" , "Extravagant or excessive" , "Luxurious" , "Lash around Vi is extravagant (6)" .)