Beautifully stated. In other words, I agree. :-) In the past, I've referred to this as the need to clear certain 'hurdles'. IMO, to be free of the sandbox, a site launched after March '04 must 'score' well in two broad areas:
#1 - ABSENSE OF NEGATIVES
Show minimal evidence of being "overly SEO'd" (working definition of "overly SEO'd": too many co-existing indicators of optimization, probably determined by crossing number of infractions with intensity of each infraction).
#2 - PRESENCE OF POSITIVES
Exhibit sufficient "indications of quality" to be excluded from sandboxing.
And #1 and #2 are not static.
My guess: Go far enough with the NEGATIVES and you may never get past the algo. But the more 'credibility' you establish via evidence of POSITIVES, the greater the likelihood that you can overcome the measured negatives.
(Sidenote: This IMO is why some blogspam has worked. The perceived positives <overwhelming number of IBL's> were sufficiently great as to overcome the measured negatives. Seems that they've fine tuned that problem a bit however.)
And yes, it seems that sites "pop out" in bunches because of tweaks to the criteria in the algo and filters, as we easily seen with Allegra.