The SR series haven't really hit any collectible value yet and probably won't. Don't get me wrong, they're great guns and I've owned full size and compact but run of the mill plastic guns won't gain much if any value.
If yours is one of the original ones it may be even less. If it has the O shaped mag release instead of the D shaped mag release then it indicates the older model, possibly pre recall that has a worse trigger than the D models.
Just adding a knife doesn't do much...