An indivision scandoubler would be better option and easier to get if your just gonna be playing games or general workbench use i would think.
If your gonna start using the 4000 as a main computer to do internet and other stuff then a vid card is a good idea.. Keep in mind if its a model without a scandoubler then it wont pass through the native amiga resolutions for games and non workbench apps. etc..
Options:
1. An amiga zorro card, picasso IV is the ultimate, built in sd/ff.
, others , cybervision64,cybervision64/3d,picasso2, gvp spectrum etc..
2. A pci bus board with a pci voodoo3/4/5 etc.. No scandoubler but higher res graphics.