What is the appeal of the Denon 103 cartridges?

I think each cartridge must be good or bad in its original form, each time someone changing a cantilever from one to another the result is a different cartridge and the sound is not as expected by the designer of the original cartridge. Some people think they are always smarter than cartridge designers or they think their re-tippers are smarter than people who actually design cartridges. The problem is that a cartridge is not good enough, simply not the best model or does not sound as expected. 

Many cartridge designers explained why it can be a disaster, refirbishing is very bad idea for almost any high class cartridge. For a low class cartridge it can work, but If a cartridge is not good then it can be replaced by a much better cartridge, no need for frankenstein that retippers are offering. 

Stick to the original cartridge and if you don't like it buy another original cartridge. This process can take entire life, because hundreds of great cartridges are on the market (lomc, mm, mi, moving flux, strain gauge etc) and you never know what you like until you will buy it! Some carts like IKEDA or Decca does not have a cantilever at all. 

  

Had a 103D and a Zu modified 103 and honestly, while I could certainly enjoy music with either, neither one was anything special and the Zu definitely wasn’t so much better than the standard 103D to be worth the additional price.

For the same money there are Audio-Technica cartridges that sound more enjoyable (to me), and though many would love to believe that there is some special inexpensive cartridge that is equal to or better than the multi-thousand dollar cartridges that’s pretty much a wishful thinking myth, in my experience.

Good to consider articles at this link: https://www.stereophile.com/content/denon-dl-103-phono-cartridge
From years past. Also maybe unfair to describe Denon 103 and 103 R stylus as simply conical. It is special Denon cut diamond - described as naked square cut. Under microscope it looks like it has been cut to a pyramid with the sharp apex of the pyramid being slightly rounded to sit in the record grooves.  Conical diamonds look different under microscope, more rounded and much blunter. 

Denon 103 and 103 R can sound best in wooden bodies, with appropriate tonearm mass.  Set-up is important, but value for money is very well rewarded.

The compulsion of language and grammar. The ''S is P'' sentence form. Aka ascribing properties to specific objects. But we
can't say anything about any cart without comparison with other
carts. This however imply relationship between objects. For
relations however the ''S is P'' sentence form is not suitable.
''Brother'' for example does not describe any object or subject
but refer to an family place in a  family ordening. Or, to put
this otherwise:  ''better than...'' relationship assume comparison. 

IMHO it takes a heavy arm for that low compliance (I use a Jelco 750 for them).  Proper use of a step-up transformer really helps as well, and there is a lot of disinformation around.  Some hints:

 1) a transformer has no set impedance; it reflects the load impedance back to the source as a function of turns ratio.  There are calculators on line. 

2) You lower the load impedance from the MM's typical 47k by adding resistors in parallel.  Some people solder resistors across RCA plugs and insert them into Ts at the preamp's MM In.  Others find or make a switchbox for this purpose.

3)The thumbrule for desired reflected impedance at the cart is to start at 2x the DC resistance and go up.

4) For a DL-103 (40 ohms) you want to start around 80 ohms.  A common turns ratio for use with DL-103s (and others) is 1x10.  A 47k MM input would reflect as 470 ohms; we need 8k, to reflect as 80.  A standard E96 1% value of 9.76k in pararallel will give you 80.1.  I usually wind up at about 100 ohms (Denon says >100); 12.7k yields 99.98 ohms.  15.8k yields 118 ohms...

A caveat:

The reflected impedances only work that neatly (factors of 10) for 1x10 transformers - there are square roots in the formula.

All vintage Denon SUTs are 1x10 or have that option via switch.