Is there a way to create linear spirals?

The Twirl method is indeed a bit wobbly at the center and at the points where the twirl begins on the line. The spacing of the turns seems accurate and even, though. In looking closely at the anchor points and control handles, the ones on the turns are parallel, while those at the center and the outside aren't quite parallel, which is what seems to cause the wobble.

I agree that Illustrator needs a better way to make spirals. I don't use them all that often, but it's frustrating when I do need one.

The Twirl tool produces a decidedly wobbly result much like the Twist filter and very inaccurate near the centre. You can't control the number of turns properly and anchor points get produced more or less randomly it seems. I don't know why these inaccuracies creep in. Seems like accurate Archimedes spirals are a thing that the Illy people haven't addressed properly. The smoothest result so far is my second example, the old "compasses" method, even though it isn't a true spiral.

Another technique: use the Twirl tool on a straight line and then cut it in the center where the spiral turns back on itself. Adjust the Twirl Rate to control the spacing of the windings.

I had a happy accident with Steve Fairbain's first technique. He's right that it's a bit wobbly, but if, after doing the Distort/Twist, you press Cmd-d to duplicate the transform, you get a wave-type Greek key design. Pretty cool!

FreeHand's spiral tool can be set for even spacing. It's a breeze to use. If you have a copy of FreeHand you could draw the spiral there and copy it into AI.

FreeHand's spiral tool would make a good feature request.

http://www.pixentral.com/show.php?picture=1E9ZX9RpRhpK0xqMo3E4cZ6bJTZme0

Here's another way for what it's worth. It corresponds to the old way of drawing a "spiral" with a pair of compasses.
Draw a set of concentric circles with the same increment between sizes. For example 5, 10, 15, 20, 25, 30 units.
Cut and paste the bottom halves of the circles and snap them so that they mis-align by 5 units. Now you've got a double spiral, so you can delete the red bits, Now join up the ends (Join - Smooth) and you've got pretty much what you're looking for. Of course it's not an exact spiral but good enough to fool the eye.

The trouble with this method is that the spiral gets increasingly inaccurate the more often you apply the filter. Not sure why, but I think it probably has something to do with the positioning of the geometrical centre, which moves slightly each time you apply the filter.
If you apply the Twist filter far too many times you will find that the path sometimes turns back on itself, forming little loops. This shouldn't happen and even Simplify doen't get rid of those loops.
Something is obviously a bit wrong with the way the filter is written.

Steve
Wow...! what a smart solution....brilliant.

I cracked this one for you, at least sort of :-)
With the pen tool draw a straight horizontal line. Colour the stroke only. Copy-drag it so that the left end of the copy snaps to the right end of the original line. "Un-colour" the copy.
With both lines selected go to the Distort/Twist filter and enter 360° (or 90°, or 180° - it maketh not much of a diff). Apply the filter as many times as you wish. Now select the uncoloured line and delete it.
Bingo-ish.
I notice however that the line is a bit wobbly in some places (the filter doesn't work very accurately and scatters anchor points here and there along the path), so the line will need a bit of adjustment. Object - Path - Simplify will get you most of the way.

Alternatively (if you're good at drawing with the pen tool), you could make a guide of the original spiral path and use the pen tool to re-trace it smoothly. In which case it would be useful to find the centre of the spiral and snap horizontal and vertical ruler guides to it. That way all your new anchor points will be aligned properly and you can hold down Shift as you drag out the handles.