What is the Spinbase not doing for you?
The Spinbase Max just seems to go a bit lower than the original Spinbase so it's not worth switching too especially not for $500 since if you want lower bass then add a powered subwoofer for much lower bass that you can feel.
Do you have a subwoofer size and budget in mind?
No need to change cartridges, you can upgrade just the stylus to OM10 or OM20 or LP Gear OM10 $39 is a good value.
If you are looking for better sound quality and you must have a vertical setup under the turntable then you could get a turntable stand and place a better pair of speakers in the top vinyl storage area.
Klipsch the Fives powered speakers with a built in phono preamp.
Or an amp or receiver and passive speakers:
The top record storage shelf may even allow the tweeters to be at your seated ear level, scroll down to the speaker height section.
If the speakers must go in an alcove then at least bring them to the front edge of the surface to prevent reflections and give the speakers room so they are not up against the back of the alcove. The term "bookshelf speaker" is a misnomer, these type of speakers are designed to ideally go on speaker stands. Speaker Placement Guide: Get The Best Sound From Your Stereo
If you have a small to under medium size room then an option is to go down a size to 4" mid bass driver speakers.
4" Klipsch KD-400 $329 $159 powered speakers with RCA audio cable input for the turntable plus Bluetooth for streaming audio from a smartphone, tablet or computer, plus digital optical input for a TV, plus USB input for a computer.
Or is you get the mini amp or stereo receiver then passive 4.5" JBL Stage 120 $149. Or 4" Micca RB42 $149 go low for their small size. Or 4" Klipsch R-41M $119.
For a small room or a desktop setup smaller 4" or 4.5" are an option:
4.5" https://www.amazon.com/JBL-Woofers-Alluminum-Tweeter-Bookshelf/dp/B07TC79BNW/
4":
Will they be on a desk to the left and right of your monitor or laptop?