Lots of good answers here. As @Phil Starr says, your setup is probably capable enough to handle the venues you are currently playing. It's not your normal 1x10! Of course, the only way to know for sure is to try. If you do find that your amp is struggling, the most effective way of getting extra headroom is adding another Monza. This will give you an extra 6dB (in theory) - a noticeable volume boost - and you'll have the option of using one or two cabs depending on the gig. It shouldn't prove too expensive, as you'll then be able to sell your 2x10.
Unless you're playing reggae and boosting the bass to its max, a Monza stack will cope with just about anything. Any louder, and you'll definitely be going through the PA.
As far as amps are concerned, it might be worth looking at more powerful amps once you get a second Monza (and even if you don't). I always assumed that the sweet spot was around 500W into 4 ohms, and I've owned most of the well-known brands like Markbass, Aguilar, Ashdown RM as well as heavier amps like Trace, Behringer, etc. In my opinion, there wasn't very much to choose between them. I ended up buying a Veyron and stuck with that for a while. However, when @Mertonplonked his Trace TE1200 on top of a Monaco at the SE Bass Bash last year, the difference in sound quality was immediately noticeable. More punch, more clarity, greater definition - a more 3D sound. Overall, it's much more enjoyable to play through. My Precision with flats now sounds like Sean Hurley playing through thousands of dollars of studio gear - or at least it would if I could play like him.😃
The Trace was quite expensive but I notice they are now selling for around £850 new. To mitigate that price somewhat, it includes an excellent two-band compressor that is much better than any other built-in compressor I've used and on a par with £150 pedals. I bought the Trace from @BassAdder60, who seemed to prefer his Eich T900 to the Trace - so it might be worth checking that one out, too. Other expensive brands, like Mesa and Bergantino, are available but I haven't tried them.