Disclaimer: I like d20 Modern quite a bit, have defended it in various on-line fora, and personally prefer it to Spycraft 1.0 (which I do own) for various reasons. I own the d20M corebook and a number of supplements, both official (everything prior to d20 Past) and third-party (all of The Game Mechanics' print stuff; Ultramodern Firearms; Blood & Fists; Dark Inheritance 1.0; the first 3 GWd20 books; and DP9's Mecha Companion hardback). So I'm not coming at this as any kind of d20M hater or as a "fanboy" of Spycraft or AEG.
I think in one sense it's true that Spycraft 2.0 is unlikely to overtake d20M in straight sales numbers for a variety of business reasons that have nothing to do with content. OTOH, in terms of mindshare -- especially among the "hardcore" gamers that tend to dominate online discussion -- I think SC2.0 stands to make real gains. There are a variety of elements in d20M that have been received less than favourably: the non-archetypal basic classes, the convoluted multiclassing required, the handling of firearms (esp. automatic weapons), the unarmed/nonlethal combat and damage systems, the blandness of the feats in the corebook. SC2.0 addresses all of these, and adds a level of generic applicability that was lacking in SC1.0. It also features a vehicle chase system that is much more popular than the default handling of vehicles in d20M, such that it's been much emulated and adapted in d20M third-party material.
I think the real question is support. When you look at official support for d20M, the trend is downwards from thick, comprehensive hardcovers to thin softcovers of debatable value. For that matter, I can't look at the decision to make d20F thinner than UrbArc as anything other than a loss of confidence in the d20M line by the beancounters at Wizards. The real strength of d20M is third-party support, though that seems to be getting more and more thin on the ground in terms of print product. Spycraft 1.0 wasn't entirely without third-party support: Paradigm Creations published Most Wanted (a compendium of NPCs) and Mythic Dreams migrated Dark Inheritance from d20M to the "Powered by Spycraft" license for DI2.0. If AEG can (will?) make it easier for third parties to publish print or PDF product under the PbS license, Spycraft 2.0 could make a dent in d20M's numbers. If a good d20F analogue was published for SC2.0 -- especially if it made ample use of existing OGL material, some of which IMO is more solid than the d20F content -- it could be a real winner.
Either way, more choice for gamers is good.
KoOS