I just bought a Speedy 30 and a mono PTI wallet as well!
I got the speedy from Saks in Cincinnati and the PTI from elux. Does your PTI have an elasitc penholder? Just curious..
As for your question, the Lockit is wonderful but you have some lovely pieces to enjoy..try and pace yourself and enjoy.
Keep & enjoy your current bags, if you sell them to fund another purchase and later want to buy them again it may be after a price increase so it could end up costing you more.
Return the cosmetic, and put that money towards your future savings to purchase the lockit. The speedy is a classic and the wallet will last you forever, I use my LV mono wallet with all my bags even my Chanels.