You system looks great! Very well chosen and balanced, so it’s hard to pick a real soft spot, which is why you’re going to get a dozen different answers.
Upgrading your cartridge to a "next level" is always a solid upgrade in your position, so the very cool looking Umami should indeed be a tempting option. If you want to try something different there are nice deals on new Benz cartridges in the classifieds here. I picked up an LPS myself recently and can highly recommend it; superb for the money! (Note: I’m not saying the LPS itself would be a great choice for a Tracer, as you will likely need a heavier counterweight for its very!! heavy 16g mass, but other models in the upper line like SLR should work great!)
Next I’d look at that RP-1 (I have a lot of experience with Rogue gear, though not with that one). I’ve heard it said, by someone I trust who’s heard all the RP’s, that you really want to get up to at least the RP-5. Especially with your level of gear, and those M180’s. There are also great all-tube used Rogue preamps to look for: Perseus Magnum, 99 Magnum, Athena -- though you will lose the digital volume, I personally prefer the Athena’s sound to even the top of the RP line.
Next look at phono stage. I moved on from the ~ $1K solid state phono stages a long time ago, in favor of tube stages, and loved the result. The new Trumpet MC is tubed (well, with a JFET front end) and potentially a legit giant killer at $1K. It’s a great choice if you like a warm, open sound. Plus it has loading options to work great with even the Benz ruby-plate cartridges, which would struggle on a SUT. I bet say a Benz SLR plus Trumpet at $3K total would blow many people away. But there are a lot of great tube stages out there if you want something different.
Further down the line, if you look at Dark’ing your already excellent M180’s -- personally I’d advise you rather to trade in towards a Zeus or Apollos. I’ve had sets of Apollos both normal and dark, and the bigger jump was from M180 (which I’ve heard in comparison to my Apollos at my dealer’s) to Apollo/Zeus rather than from Apollo to Apollo Dark. It’s psychologically nice for me to think of those high-end caps in the Dark version, but personally they didn’t rock my world quite as much as I’d thought they would for the upgrade price.
