Can good soundstage be had in small room

Try small speakers, spaced ~55-65 degrees b/ween them, 2-3ft from their back wall and listen nearfield. You should be able to get a good image.

Can you layout your room to where you can place your speakers across the 18' dimension?
If you could place your speakers 4.5' away from each wall, that would give you 9' of spacing between the spkrs. Place your sitting area on the back, or very close to, the rear 18' wall. You'll have to play with the spkr distance off of the now "front" 18' wall. Avoid placing them at the 4.5' location , because that would have them (the front/center of the drivers) equal distant from both the front & side walls, which can not be so good. Try starting about 3' out. Ideal should be at the 5.5' mark. That will give you a "nearfield" setup and pretty much remove the first side-wall reflections.
If you can work with that arrangement, you'll be suprised at the soundstage and imaging. You'll have to make several adjustments to the toe-in, depending on your speakers. Having a $19 laser level from Home Depot helps tremendously in getting both spkrs set evenly.
If you try this, get back with your listening report?
Good luck and happy listening!
Try That setup

You should get a pair of near field speakers since they're less sensitive to the wall behind them. I'm currently using ATC SCM10 passive monitor speakers. If you have no other furniture in the room then you can consider larger coaxial or horn speakers. However, the placement will be harder than the near field monitors.

Yes, check out the web link below for Cardas method of speaker placement.
http://www.cardas.com/insights/index.html
Select "Room Setup" on the right side bar. I 'm using this method in my smallish dedicated room 15.6 x 10.5 x 8(LxWxH) with very good results ie: with quite a wide and deep "perceived" soundstage. Speakers are Platinum Solos and they are toed in slightly towards the listening seat.
Good luck.

The short answer to your question is yes, you can get a good soundstage in a small room. To accomplish this you need to pay close attention to room treatment. Most dynamic speakers can work well close to the side wall if the first reflection points are well damped. Damp the wall behind the speakers as well, and maybe the ceiling at the first reflection point. Carpet the floor. Add some diffusion behind the listening position using furniture and plants. Once that's taken care of, careful speaker placement will give you rest of it.

My sound room isn't much larger than yours - it's 12x19. I use a pair of really big speakers - Coincident Total Victories - set up on the short wall. The speakers are about 1.5 feet from the side walls, and the front face of the speakers is about 4.5 feet from the front wall. the speakers are toed in so there is about 7 feet betweeen the center of the tweeters. I listen about 7 feet from the speakers.

Given this setup I get a measured flat response (+/- 2db) all the way down, and the soundstage is one of the best I've heard.