good point. so you think its only adding a 10% improvement? if so, in my mind, definitely not worth it.
<disclaimer> Understand that is only my very rough estimation, based only on what I've read and discussed with others (including several who have done various SV front-end upgrades, a few suspension tuners, and an amateur SV racer). Also, I'm trying to put an objective number to a somewhat subjective "feeling."
It would be nice to have someone who has done springs and oil, then later added emus, do a side-by-side comparison and offer their opinion.
Here's the limits of my knowledge on this (anyone who knows better, feel free to add to, or contadict, this):
Heavier springs will better support rider weight, allow proper setting of sag, offer a stiffer ride over bumps, and control front end lift on acceleration and dive on deceleration. That still leaves damping of the spring (the rate of rebound and compression) to be dealt with.
The stock fork is a damping-rod type, which doesn't control damping as well as a cartidge-type. By better controlling the rebound and compression damping, you avoid the "pogo stick" effect of the stock forks, and you have better front-end "feel." The stiffer spring may "pogo" less and give better "feel" than stock, but the problem is still there.
The damping rod controls damping by way of some holes at the bottom of the mechanism, through which the oil gets drawn as the fork compresses or expands. Using emulators inserts an additional (and more sophisticated) variable-rate valve at the top of the damping rod, and replaces some (all?) of the holes in the bottom of the damping rod. This "emulates" the damping control of cartridge forks, and as someone else pointed out here, it has the advantage of allowing you to fine-tune the damping.
Switching to heavier oil can help with damping control, since the heavier oil flows slower through the holes in the damping rod, but it's a mild improvement and it doesn't change the basic flaws of the damping rod design. Also, there is a possibility that heavier oil can make rebound damping worse in some situations, as the slower flow rate of the heavier oil can cause cavitation within the fork.
Keep in mind that while emulators modify the damping rod design, it's still a damping rod design. In other words, emulators are also a compromise. Hence the other suggestion here that if you're going to seriously hit the track, switch to a proper cartridge-type fork (a la GSXR swap -- which, btw, should also get -- a spring and oil change).