Nice pictures.
The simplest way may be to sell the E30 project and then buy an E9 project without mandating that the values be the same or the buyers be the same.
Arde has excellent advice that you should heed. buy a decent driver and put that s38 in it - you will have a lot of fun.
all of my previous comments are based on conditions being approx. equal. comparing your e30 m3 to a similar condition e9 is no contest - yours looks very nice, but a similar condition e9 would be a lot more because of all the body work that would have been done. your car is worth more complete with the s14 in it, and should be much easier to sell for a reasonable amount complete.
lets look at values -
COMPLETE CARS
e30 m3 - in need of some work / very high mileage - $7.5k to $12k. in good to excellent shape $15k to $45k (the latter being very low miles in perfect shape) the majority of very good cars are sold between 19k + 25k. the top cars on the market right now are listed for less than 40k - and most people on the SIG think they are overpriced.
evo 2 + evo3 cars are much rarer and the cost is significantly higher - much like the CSL.
3 for sale on ebay - a very nice red car in California $25.9k buy it now, a white car in California $17.5k buy it now, salmon gray w/ s52 transplant - 15k current bid.
now for the e9 coupe (as discussed on this site)
parts car $2000 to $5000
rusty car $6000 to $10,000
good driver with some issues $12000 to 18000
very nice driver $22,000 to 30,000+
garage queen / fully restored car - $35,000 to $75,000 (at least 10 have sold in this price range in the last 12 months - all north of $40k)
CSL - series 2 BAT - outrageous
current cars on ebay -
agave (houston) - 30k current
blue (nashville) - buy it now $29.5k
red (san francisco) - 12.6k current
black (oklahoma) - $11k buy it now - kinda rusty
green (oregon) - $8.5k w/ 9 days left
ENGINES
the cost of an s14 w/ injection (not rebuilt) is $2500 to $4000, and a stock rebuild can run $7000+ and its not hard to get a non-stock s14 to 15k+. (none for sale on ebay or on the SIG - didn't check s14.net because they are changing servers / site down)
an m30 engine (bulletproof) - ranging on ebay between $290 + $1000 - rebuilt engines $3k to 3.5k.
ROLLING SHELL
the cost of a reasonable M3 without drivetrain - $5000 to $10,000 - condition questionable (not as good as yours) - the drivetrain is the expensive part to replace.
the cost of an e9 w/o drivetrain - haven't seen too many for sale in last couple of years. if the rust has been abated - $20k+ ... otherwise its the price of a decent car - $10k+ (the cost of the drivetrain is the cheap part here).
here's the conclusion of the comparison - lets assume a complete car with a value of $20k - and what that buys (body / mechanical). take the engine away and the cost to put it in - take a minimum of $6k for the m3, and probably $2k for the e9. sure this is a hypothetical comparison.
the cost to make the cars equivilent w/ similar body condition - much more expensive for the e9 because all of the trim is so expensive and hard to get in great condition. Chrome belt trim - $1000 plus install, front grilles $850 new, door gaskets $500. bumpers - expensive. comparatively, e30 m3 grill $200, no belt trim, bumpers - cheaper + easier to find in good used condition.