Windhorst explained the sole reason for the signing (whether it is popular with the fans is irrelevant)...it is to have another "good friend" (besides TT) on the Cavs roster to make signing with us more attractive for LeBron. I don't believe that there is likely to be a material impact on the Cavs' chances to make the playoffs this year. Miller looks nearly done to me, but does bring consistency when he shoots wide open 3s. CJ is younger and has a least an outside chance to be more of an impact player, but is frustratingly inconsistent in shooting 3s (except in the couple of games he was unconscious). Obviously, CJ can/will contribute more than Miller in 2013, but the question is how much more...when the real issue is what either would contribute in 2014.
If Miller is not signed, CJ is still highly unlikely to be retained in 2014. His non-guaranteed contract tells us that (as does the fact that he is likely behind Gee). So, even if KI is close to CJ, that relationship is highly unlikely to induce the Cavs to retain Miles beyond this year (and they may not do so this year for a variety of non-Miller related reasons). While I don't think KI is likely to leave Cleveland (LeBron or no LeBron), it is nonsense to believe that he would be more inclined to leave if CJ is traded or cut.
On the other hand, while neither Miller nor CJ will have much, if any, impact on the Cavs chances of success in 2014 as a player, obtaining Miller adds another piece to the presentation the Cavs wish to make to LeBron ... the absolute most comfortable and attractive place to play. Having TT and Miller would provide LeBron with 2 close friends and nobody else besides Miami is likely to offer him any better opportunity from a "personal relationship" side. Everything else is in place given the $$...an All Star PG, an All Star C (if Bynum is able to recuperate...or some additional cap money, if he cannot and a communication to LeBron that this team/owner are going out and getting the best possible players they can)...and a player they may need to use some of that cap money if they cannot (Andy), a potentially decent backup C in Zeller or a shift to TT to play some minutes there, two very young PFs with lots of upside (TT and Bennett), four different back up SFs to LeBron (Clark, Bennett, Gee, Karasev), and a shooting guard with high upside (DW) and a near winner of the best 6th man award who can shift into a starting role pretty easily if DW struggles (Jack) and a 3 point specialist (Karasev and Miller)....with lots of extra first round choices in the next few years to replenish the roster. if LeBron is looking for 4-6 more championships, this is the only team which can truly offer it to him. Even if he does not come, this team is still positioned to fight for NBA championships...although it will likely take 2-3 years longer as key players need further maturity and experience.