Jason, I have a Q3xx sitting in my garage that looks basically the same as that one and will be destined for a rehab and flip in the spring. Now that you got the grates relatively cleaned up, just take the angle grinder and wire cup brush to them and in 15 minutes, they will look great. If you are going to flip the grill, you might want to consider grinding the inside of the cook box and inside of the lid down to bare aluminum. It isn't that hard. And, since that lid looks to be in good shape, you can simply clean it up or slap a fresh coat of something a bit less boring over the top of it.
One tip on the grates is to keep an eye on Ebay. The regular mass listings are not good, but every so often an individual throws up a set that he bought in error or something and you can sometimes score a good price that way. Otherwise, you are looking at $60-$70 for a new set for the Q300 on Amazon.
I think the reason we see so many of these Q grills looking so bad is that people who buy them are looking for simple and very low maintenance (or NO maintenance in many cases). When I see a grill like yours, I just wonder if the previous owner ever even lifted the grates once.
Oh, and run the angle grinder and cup brush over the burner, then flush out the inside with the garden hose and in 5 minutes it will be purring along fine with nice blue flames.