Howard maybe, he probably could follow Raimi's world better than most and still take it in a new direction. But with his daughter in it he may not want to get too involved, though Bryce did say he came by during the shooting of the crane scene accident (the set portion) and spent all day watching how Raimi was doing it she said.
Fincher I would love to see do a Spidey movie, particularly a Lizard/KLH Spidey movie, but I don't think he'd touch the franchise with a ten foot pole now that it is so defined by Sam Raimi. Taht I think is the key problem. The man did three movies and his look and auteur stamp is the Spidey movies and even if the new guys are given free reign, it may be artistically stifling for them to try.
Some fans fail to realize this, but not eveyrone wants to direct a Spidey movie, particularly if it's the third sequel in the franchise. I also think Sony has set a release date (if only internally) and making that releae date will be more important than anything else for them. Raimi's biggest obligation to Sony was making sure that SM2 and SM3 were ready for release dates. Sony/Ziskin even "joked" (more half-joked) that after letting themselves agree to Raimi delaying SM2 to July from May to finish the SFX and polish the movie some more that SM3 "WOULD" be making it's early May release date, because some were superstitious at Sony that SM2 not opening the first week of May was the reason it didn't do as well. Maybe SM3 would have flowed better if Raimi had two more months in the editing room, but his date was May 4, 2007 and he had to make it.
If Sony is even quietly gunning for 2010, that is of the highest importance now.