I'll recommend USEFUL, which some find boring, but truly useful is never boring — well, at least utility-builds get ME excited.
EQ, you can do so much with EQ and it fixes so many other pedals' *ahem* shortcomings.
Whether playing in your bedroom-studio or live, EQ can save your sound.
Given the criteria set forth in the OP, I do NOT recommend an
Equilux Mini for your next build, but here's some lower parts-count easier-to-accomplish EQ-ideas to work up to the Equilux...
Whether you play bass or guitar, this is useful — but a good HPF is particularly useful for bass-players (this also has an LPF to tame highs):
Compare to Broughton Audio Low + High Pass Filter
www.pedalpcb.com
Dial in your sweet-spot, dial out low-end rumble or feedback from your semi-hollow... lots of good here in HPF/LPF land.
For cutting through a mix, making a solo pop out a little more, the Mercurial Boost has proven popular with the forum's guitarists and bass-players alike — mo-mids-mo-better:
Compare to Catalinbread Varioboost
www.pedalpcb.com
If that Mercurial's still a bit much, no need to feel like a pariah...
A lower-parts count mids-booster that's less daunting, but EQually exciting for the freqs:
Compare to Way Huge Tone Leper
www.pedalpcb.com
Based on the WayHuge Tone Leper, which is basically a Craig Anderton Frequency Booster, this one's lots of fun to tweak on the breadboard before building.
For less utility but MOAR Fun EQ, a cocked Wah can also poke a solo out in front of the mix:
Fixed Wah
www.pedalpcb.com
The only out-of-ordinary part to push out of the comfort zone is the transformer.
If you play bass at all, this is a simple but great sounding preamp — heck, probably sounds great on guitar, too:
Compare to ElectroniX / Zeibek Submarine Bass Guitar Preamp
www.pedalpcb.com
