Just the rear one will drastically improve it. A lot. And its very easy to do. You can either get the VF Engineering mount, or if you are a DIY kind of person, get the polyurathane inserts from Energy Suspension, and modify the OEM mount.
I've had something similar happen once. I shifted hard from 1st to 2nd and it sounded like something hit the firewall, but I haven't had any concerns, and I haven't been able to recreate the sound. Must've just been some good asphalt. 
$19 bushings and about 3 hours work. It's pretty easy, and a great mod. I did it two months ago and no more banging. There is a little more engine noise and some vibration during decelleration, but it's worth it!
The mount is below the transaxle, going towards the rear of the vehicle. Easy to see, it looks like a twisted dog bone.
No AC and the only time I notice it is on deceleration with the clutch in. As the engine rreaches idle, it shitters for a second or two before it hits idle. No big deal at all. Far better than slapping the transaxle off the dogbone every shift!
I put the rear mount (energy suspension) in and it was cheep. 20 bucks give or take and only took an hour and a half to do and I had never done anything like that before so its easy enough. I had a press to use to get the stock bushings out of the mount. It does shift a little better and all that but the shaking at idle was worse than I was expecting even with AC off. I think it has died down (bushing wears in a little?) since I first changed it. it was really bad it shoock the pedals on my feet!
I've got the rear mount on my dura 2.0 with CAI and it is nice...a slight vibration at idle but other than that, you DEF notice a difference on take off and how it holds the motor down better!!!! I dont have AC so I cant tell you about that....def worth the money, and it really only takes 10 mins once you have the car in the air/jacked up. Did mine in ~25 mins because i had to jack it up in my driveway -- gravel sucks.
Yeah, every time I get a little too aggressive and give it a little too much gas and a little too early on the clutch it sounds like my engine just came through my dash. One time it was unbeliveably loud, thought I was screwed, but yeah, I'll have to look at that motor mount thing.