Yes I think it would be an upgrade over your current lens, by how much I dont know, and if it would warrant the expense.
I have the 70-300 VR and use it with my D7100, I am often wishing my pics were better. I remember using this lens on my D3100 and was constantly impressed with the photos, not sure if I am being more fussy now or not, possibly so. I still do get some great looking pics with this combo, just that a lot of the time I am left wanting for better IQ.
I am thinking I will get a Tamron 150-600 when my lens fund fills up a bit more, then eventually sell the 70-300 and get a 70-200 to cover the shorter end and get better IQ.
Sorry if this wasnt what you wanted to hear, but my thoughts are, you should stick with your current lens until you find something which is a bigger upgrade.