Bard attacks are weapon attacks, so they do get bonuses from those enhancements, just like the Nightblade gets bonuses even though they deal ranged elemental damage. However, Cadence, even though it has three pulses, only checks for weapon procs once, so only the initial hit would have a chance to proc the poison / enchant. Unfortunately, the rather odd "neither here nor there" nature of our abilities does make some talents useless to us.
What we don't get bonuses from -
- Melee boosts
- Ranged Weapon boosts
- Physical Boosts
While we can get some use out of soul points spent in assassin, you're usually better off spending them in Nightblade. Both have stealth, both have buffs, but Nightblade specializes in non-physical damage, so there's more overlap. Bard and Nightblade abilities are more like spells than anything - we can even get silenced etc while playing.