Repair or replace my subwoofer

If you’re happy with it's performance, sounds like a reasonable charge, but shipping is high these days.

I live close to the headquarters so I can deliver and pick up pretty easily. 

Looks like they're $750 new so $400 is reasonable if there's no shipping fees. Your other option is to bin it and get 2 subs like REL T5x etc.

Hayward was also close enough for me. Took mine in at 10am and got a call from them by 3;30. Maybe a slow day? I still use mine in the home theater and occasionally in a small PA system. 

The new plate is a bit more detailed with a better volume remote control but to answer your question, yes, a few subwoofers have improved greatly in both aspects but at a price.

The Super Nova benefits noticeably if it's positioned in or near a rooms standing wave bass modes. 

The Nova's lower frequency output exceeds any -6dB sub-bass woofer system.   

I think the question would center around usage. Is it exclusively for home theater? Home theater is a less exacting application where volume of bass is of higher priority. There have been advances in subwoofers in twenty years. So, if it is for two channel audio, I would look at it as an opportunity to upgrade if the rest of your system is of a higher quality. 

My home theater has two B&W 800 series subs that were made about 20 years ago. I have had them each re-taped and upgraded. For home theater they work great... I got rid of the two I had in my audio system as it got better. 

My main purpose is home theater and the earthquake has been enjoyable for action movies for sure. 

And the depth charges on  U-571!