the 968 LACKS THE KEY COMPONENT TO BECOME COLLECTIBLE.
it is not a fair comparison between the 911 and the 968. the 911 has ALWAYS been a beloved car. it has always had a very real following. the 968 has not. it doesn't even have the same following as the 944. it truly is the red-headed step child. it never caught on. in 20 years MAYBE its oddity will result in a significant increase in pricing, but who is willing to mothball a car for that long in the hope that it will? you sure can't drive it and expect it to retain value.
the M030 is not a better suspension that standard. it is far worse for all intents and purposes, with the possible exception of autocross, for the reasons i mentioned above. as for winning on the track, a very simple swap out of swaybars, shocks, and struts to even some mid-level things that are readily available now will STOMP all over the M030 on the track. it will do this without compromising the superior ride of the standard suspension. total cost, including labor, about $3k. replacement cost of M030 shocks and struts is currently $2400 plus labor. the M030 is outdated and antiquated hardware. it is horrible on the street, and second rate on the track. you would have to be a special kind of idiot to go out of your way to choose that today. 20 years ago, it was the best you could do. today, it's just not. you can have better handling and cornering, without sacrificing ride quality, for almost EXACTLY the same cost.
i have been carefully tracking the sales of the 968 over the last 12 years. M030 currently adds only about $1k to the "value" of the unmodified standard car. this is down from about $3k 10 years ago. cars with a fresh suspension, consisting of better shocks and struts are selling for about the same as M030 cars today.
auctions are weird things. they have very unpredictable results. sometimes a car will go for a lot more than it should, sometimes a lot less. even the guys doing the predicting on tv very often get it very wrong. i watch a lot of those shows.
however, the one thing that never misses is that making the jump from run of the mill pricing to "collector" pricing is that every one of those big ticket cars had a very real following. unless and until that changes about the 968, it will never make that jump.
to answer your question, i sold my car for a higher price tag, by a fair margin, than any record i can find of what any other 968 has sold for in the US in the last 10 years, with the exception of the turbo S and turbo RS. no, it did not cover what i spent on it (much of which was development cost for the product line), but i can't think of any 968 that has done that in the last 10 years.
buy it. mod it. drive it. sell it. that is what almost everybody who has ever come to this site has done, and for obvious reasons.