I'm a little over 300 hours in, so I get the feeling.
I've just started playing exclusively gold now. I'm currently grinding to get the last of my rare weapons (unmaxed manifest problems) so I have started to buy arsenal packs (and jumbo equipment packs when needed). This is because I only have two more characters to get. I was buying spectre packs in the interim, when I was playing silver games with the occasional gold. I just wasn't unlocking enough rares to make them completely worthwhile, but spectre packs are nice for all of the consumables that they can give.
If you haven't yet maxed your uncommon weapons, I would suggest to stick to buying veteran packs while playing gold games. You'll be able to buy at least three packs with every game completed. If you want more characters, you can try the reserves packs. I honestly don't have as much experience with buying these (I'm going to start after I max rare weapons).
Grinding in this game can be sort of annoying, but mostly time-consuming. I recommend to find a few characters that you are really good at and play with them to basically max out what you want.
Good luck 