I second that emotion, don't replace the guitar with a PA.
Over the years I have put together a PA worth about $8,000 bucks. A friend of mine uses the board, 2 of the effects/power amp racks, (EQ,FX,Crossovers are must haves in each) and floor wedges for his band's rehearsal space, and all of the mains, stands, 24 channel snake with 100' cable, XLR and 1/4 "cables, mics, and subwoofer are in storage in my house as I don't have the room or the need to set it up. I would much rather have spent less money and taken up less space in my home and friends' homes storing it.
Any good venue has a PA, you never want to be stuck traveling with a big one, so unless you are putting together a home rehearsal space and have a decked out space that needs a PA, or you are starting a live sound reinforcement company don't do it.
If you are going to buy something for an acoustic duo, buy a small one, and there is nothing wrong with a powered mixer. In fact, it couldn't be more right. It makes your life so much easier, trust me, I lugged my huge PA around for years doing private parties and it was a HUUUUUUUGE mistake not to have something smaller, lighter, and easier to set up and run. Not to mention, the powered mixers are much cheaper and you should spend your money on really good microphones and EQ's for your acoustics first otherwise it is all a waste.
Until you do it a few times, you have no idea what a pain it is to carry around three racks each with a very heavy power amp at the bottom. 2 mains, a sub, a pair of floor wedges, snake, Speakon cables, mic stands, everything. It is overkill. Not to mention the pain and cost of maintenance.
My advice is to find something light and easy to set up. Something that doesn't require a sound man to adjust while you are performing. Spend your money on some very nice vocal mics and EQ's for your guitars.
That being said, don't get rid of the axe.
There are only two mantras. Yum and yuk. Mine's yum.