Originally Posted by Alrik Fassbauer
Is it worth to buy additional inventory space via the DDO shop ?

No. Get extra packs by doing quests for Coin Lord favor.

Originally Posted by Alrik Fassbauer
Plus, is it worth to buy additional "Adventure Packs" ?

Yes. Be choosy about which ones you buy, as some are extremely worthwhile and others are pretty much crap. Good packs for lower level toons are Sharn Syndicate and Tangleroot (good XP, decent loot, good favor). Many recommend Phiarlan Carnival, but I don't have that one. I enjoy Catacombs quite a bit, but I think I'm in the minority on that one.