that's what I don't like about conspiracy theories... they sound fairly logical or evident
but if you take a few steps back and regard the whole issue, they start looking less logical and dubious.

everything you say kinda makes sense. But wives normally don't kill their husbands, and the police should have no problem to find out if it's murder or not.
the angle of the shot, for instance, should be different if it's suicide.
It's also possible that someone wants to blame Courtney Love for some reason

it's logical, but it's no evidence. If it was evidence the case would already be closed... in fact, maybe it is closed coz the police has already proven that it's suicide.
(or maybe they're just saying it's closed while they're investigating, as you suggested)

but it doesn't even matter anyway. It doesn't affect us, we don't even know Kurt Cobain. Nobody would give a shit if he was an unpopular person.
Instead of thinking about things like this, things that don't matter, we should think about things that affect tons of people, like corrupt politics, economy, poverty, etc