phono stage upgrade from Denon pre-amp

I've been using a Denon PRA-1500 stereo pre-amp for a while now, feeding a Rotel RB-980BX hooked up to a pair of Onix Reference 1.5s. This Christmas I received a Technics SL-1200MK2 as my first TT. It came with an inexpensive AT cart (8008 I think) and I've so far been using it with that, hooked up to the phono input on my Denon pre-amp.

Played some brand new LPs (Dr. Dog - FATE, of Montreal - Skeletal Lamping, My Bloody Valentine - Loveless, all 180g) and the sound is pretty great I think (although I'd say kinda on the thin side and I have to turn up the volume on the Denon past 12o'clock for even reasonable volume).

I know it can get way better than this though, which is why I'm planning on buying a Sumiko headshell and a Denon DL-110 cart as my first upgrades. I'll then rewire the tonearm with cardas 33awg, get a better mat and possibly the KABUSA fluid dampener somewhere down the road.

Anyway, my question concerns phono stages, and that is: how much would I have to spend to better the PRA-1500's by a significant margin? I have no idea how good/bad the Denon's phono section is supposed to be. I have a feeling I should definitely upgrade the cart, arm, etc. before worrying about this but I'm curious.
Look at the PRO-JECT phono stages. They have 2 tube and two transistor ones. The Tube Box 11 SE has outperformed ones costing many times more at $699. It would be a very big step up. The cheaper ones are all good in their price range. The Denon 110 is quite good. I got mine new on eBay from Yogi for $110. I would say that in the PRO-JECT line the middle two would also give a good increase in performance.
Bottlehead seduction. I ran a dl-110 thru mine for a while, good match.
I have heard good things about the Project, never heard it, but the bottlehead has quite a dedicated following, and is very tweak-able.
You can usually find them used for around $300.
I'll leave it to others to recommend phono preamps for you -- most of the ones I have heard or know about are in the $1500 to $3000+ range. What I will comment on, however, is your remark about having to turn the volume knob up to or past the 12:00 position. Is this a concern for you? If so, you might think about how the volume knob works. Essentially, it is a potentiometer/attenuator. At the full "open" position (i.e., turned fully clockwise), there is essentially no attenuation of the output signal to the amp. Conversely, when the volume is turned all the way down (fully counter-clockwise), all of the stages in the potentiometer are "in line" to reduce the signal output. Understood from this perspective, having the volume control turned up to 1:00 or 2:00 is indicative of a better-designed volume control function (greater range of movement, which enables subtler adjustments to volume). Far too many preamps / receivers have their volume knobs set to play loudly in the 10:00 to 12:00 position, which means that you have a much reduced range of rotation for the volume knob. Unless you have concerns about the QUALITY of the sound from your pre-amp, you don't need to worry about setting the volume knob above 12:00.