It really is a shame artillery is getting sidetracked in modern armies. But with the lack of a big enemy who you might fight in a costly and long war, quality over quantity, even at an expense of a great financial strain, does seem to reign supreme. In case of a large scale ground war, I am pretty sure artillery would prove it's worth, after large portions of cruise missile and guided bomb stocks have been used up.
Greatest advantage of towed artillery is it's small weight. Even though on the battlefield itself it's less maneovarable than SP, making quick short to medium range transfers by helicopter or packing in dozens of artillery pieces in a C-17 for example is something not achievable with SP artillery.
Thing is, SP artillery through history, and this counts in even modern wars like the gulf war, has rarely been used to maximize its advatages. A battery of guns gets deployed and then it remains at station, firing rounds just like towed artillery would. Yes, deployment time is shorter than towed, protection is greater, but over the average time such a battery is engaging the enemy the number of projectiles is more or less the same as it'd be with towed artillery pieces.
Basically, towed artillery has its uses and i don't see it disappearing. It is on the commander and the strategists to decide which artillery would be more useful in which situation.
A question for the Fin. While i see the logic behind repair vehicle being more expensive in a SP artillery battery, why do you say the command vehicle and especially the ammo supply vehicles would be so much more costly than their counterparts in a towed battery? I mean, 6.6 mill compared to 1.1 mill?