Upgrade? DD 210-s4 to DD 610-d4?

I’ve just bought a new box to replace my old Best Buy angle sealed box. It’s a Q bomb 1.4ft with a square vent tuned to 39hz I think. My pioneer amp does 300 watts at 4ohm and 500 at 2ohm. I won’t be attempting to run to 1ohm.

http://www.qpowerinc.com/details.aspx?product_id=44

Space is the limiting factor as well as cost. I can’t go much bigger than the 1.4ft box I have. My trunk is too small to accommodate the box and my kids stroller. He’s special needs and won’t be walking anytime soon if at all. I wanted to get a bigger box tuned lower but… yeah.

Would the higher quality speaker really play better? The speaker I have now was $100 back sometime around 2006ish.

DD doesn’t have an archived page for my current speaker. I found this though.

https://speakerboxlite.com/subwoofers/dd-audio-dd210-s4/specifications

This is what I’m considering.

https://ddaudio.com/600-series/power-tuned/610f/

Maybe the 510 would be a better option?

https://ddaudio.com/series/500-series/?status=2&global=2

Or… is this wasted money? Should I wait and get two of these to put in a sealed box and a new amp? I’m certain this would be a far more impressive option but when I floated the idea of spending $600 then needing a new amp eventually my wife made a face. It’s just too much for us to spend ~$1000 on bass for my car. The economy or whatever.

https://ddaudio.com/series/sl700-series/?status=2&global=2

I’m aware there are a million options for this stuff. The only other local shop I know of sells massive audio and I’d rather go with DD. I’m one of those guys that buys local whenever possible. This is too long of a post. Thanks for reading.