Guild Wars 2

I’m thinking of going grenade for my engineer. I’m wondering if I should spend money on getting a good weapon.

Does weapon dms/stats affect the grenade damage?

Of course yes! The better the weapon is, the better your damage output will be.

Stats, yes. Weapon damage, no. Kits have their own base weapon damage, which is roughly equivalent to rares of the same level that the user is. However, they use the stat bonuses and sigils of your equiped weapon(s).

Edit:
http://wiki.guildwars2.com/wiki/Game_updates/2013-01-28#World_Polish_.E2.80.93_Other

Best gear in terms of damage output for grenades is Rampager (Power, Precision, Condition damage combo)

Rozbuska.5263:

Best gear in terms of damage output for grenades is Rampager (Power, Precision, Condition damage combo)

The main caveat being the condition mechanics in this game. Rampager’s is the highest DPS if you are the only one hitting multiple targets, but as soon as your conditions get overwritten, your DPS drops quite a bit. Any low-add-count boss fight would be a great example of considerably lower output, with multiple people on one target.

Rozbuska.5263:

Best gear in terms of damage output for grenades is Rampager (Power, Precision, Condition damage combo)

I use Berserker with grenades. I prefer a higher critical damage over conditions.