Upgrade from Technics SP25

gotog, this is not to suggest you upgrade your table, Raul and chakster have given good advice.

However if you are not aware I thought you might like knowing more about your table.  Technics offered three SP model tables at different price points.  The top was the SP-10 Mk 2 (initial SP-10 underwent many upgrades), later upgraded to the Mk 3.  Next downward was the SP-15.  This was also a high quality unit with a large heavy platter, fine tune speed adjustment but with onboard power supply.  It was also good enough for studio use as well as consumer applications.  Then came your SP-25.  From my reading that is essentially the motor and electronics from the famed SL-1200 series.  Most parts are interchangeable.  However it was a motor unit only, allowing for selection of separate plinth and tonearm.  As the reputation for the SL-1200s suggests, your SP-25 can punch above its weight.

All this is offered for future reference.  I wouldn't spend $2.5K for a cartridge in your system but there must be many upgrades, including a retip of your Denon.  You didn't say how many hours on yours but the conical stylus will not likely satisfy anyone looking to dig deeper and extract more detail.

Good luck. 

There was an SP-20 released in 1976 which is exactly the same size as the SP-10 mkII, but without external power supply. Actually very nice turntable, i have posted about it on audiogon few years ago.  

I know it's fun to change the turntable, i did it many times, nothing can beat the DD Luxman PD-444 in terms of usability if the owner would like to swap the tonearms. 

In my opinion changing the SP-25 to something else will not change the sound if the tonearm and cartridge are the same. SP-25 is a nice DD with stable rotarion and high torque, if the plinth is nice then it is a great combo. 

The most important is the cartridge and sinergy between the cartridge and tonearm. Definitely the phono stage too. Turntable just rotating a platter with a record on it. 

I've owned two SP-20 and one SP-10 mkII. You can upgrade your SP-25 with a nice air craft alloy mat from SAEC, the SS-300 is a must have between the LOMC cartridge/record and the platter if the motor is right under the platter. Micro Seiki CU-500 is even better. 

I purchased an SP25 with an ATP-12T arm inside of a Technics wooden plinth in rough shape about 4 years ago with to sole idea in my head of flipping it. I refurbished it and did some minor mods.  When I was done I had a hard time letting it go.  Performed quite well.  I used it for a year before selling it. 

Here is a minor, simple and inexpensive change that was audible on this table.  
On the bottom of the plinth,  ran industrial hot melt on all seams.  Took Butyl tape and dampened everywhere possible on the bottom of the plinth,  it added a fair amount of mass, but the plinth was noticeably deadened. Took butyl tape and put a thin layer on the bottom of the platter. This helped dampen the motor from platter nicely.  I did not rewire the arm, but I used a litz tonearm cable,  it was a nice improvement over the AT cable. These mods won't necessarily cause your table to dig deeper,  but things are tighter, more focused. Look at a different cartridge to dig deeper or pull more details out of your music.  
I hope this helps,  Tim 

gotog, chakster has mentioned the SP-20 a few times now.  It may be a fine motor unit, I've never seen one.  But depending on where you live, I believe they are very rare in the US.  Also you don't find the backup such as a service manual at VinylEngine as you will for the SP-10/15/25.

If you do reach a point where you'd like to upgrade your SP-25, then either suggested mods to it or step up to a higher Technics or other quality DD such as Luxman, Kenwood, Denon, JVC, etc.  However know that Denon and JVC can have difficult repair/restoration issues.  But when working all reports are they are fine tables.