Which do you think is the larger market, acoustic percussion or DJ gear? Acoustic or electric guitars? Digital versus acoustic pianos?

No need to guess. NAMM assembles those numbers every year, although the most recent figures are accessible only by members. Here's a link to the latest report that's publicly accessible (data through 2010).
For those too lazy to follow the link, here are the answers to the above questions:
- acoustic percussion $479M, DJ gear $104M
- dead even: acoustic guitars $419M, electric guitars $420 
- acoustic pianos $287M still king (although down by 50% a decade ago), digital pianos $130M

Other interesting nuggets...ukuleles are a $42,000,000 a year business and growing...printed sheet music is still selling as strong as ever ($545M)...hardware synthesizers are also still strong ($106M)...instrument amplifiers are down ($230M, maybe because everybody's buying smaller guitar amps?)

Interesting. Thanks, Bit.

bitflipper


...instrument amplifiers are down ($230M, maybe because everybody's buying smaller guitar amps?)

The Who has cut back on their touring.

" ukuleles are a $42,000,000 a year business and growing" - well at least until  the hipsters get bored of them. 

nice statistics, now wonder why my profession is on demand if they sold so little keyboards... 

I didn't see accordians or bagpipes mentioned...

bitflipper



instrument amplifiers are down ($230M, maybe because everybody's buying smaller guitar amps?)

according to the link multi track recorders are 98 million. People are still using those things? lol computer music products comes in pretty strong at 385 million.
 
Instrument amplifiers may be going down because more people are pluged into the P.A. systems and the are not using the amp at all. I switched from using a guitar and a bass amp to going straight in. That seems to be the trend now. A lot of my friends have done the same thing.

The total took a dive in 2009. And Sound Reinforcement seems to be the most at $717 million. Must be playing live, I suppose ??

Churches are the big sheet music buyers.  The ones with big choirs and orchestras have to buy all the players and singers books and such things..... it's illegal to buy one and run it through a copy machine on site to save money...... and they do not give those books away. 

Drums..... The fact that there are multiple drums in a given kit would seem to be a good reason for more spending on percussion vs guitars..... Even a cheap kit with cymbals will set you back the cost of a fairly  nice guitar. While for a guitarist, a few hundred bucks (under $500) gets you the guitar and a fairly loud amp these days..... 

Guitars are good business for ongoing consumables Strings and Things.

My turnover always reflected fewer sales on Drums but similar proportions on the figures to that chart so basically I'd be selling 10 or so guitars to get the same turnover on a shiny new Gretsch kit.  That was many years ago now too and I was considered a specialist for drums and perc. and even supplied a few Marching Bands.  I never did Hi-Tech gear then though.

It is the turnover on consumables that keeps most small business afloat though and guitarists make the most regular repeat customers by far, many replacing strings on a weekly basis.