Without knowing what you use the software for it is very difficult to say for sure but when you look at what has been added since 4.5 there is a good chance that there will be something in it for you.
As has already been said you need to look at the update info for 8, 8.5, 9 & 9.5 to get a proper picture of what has changed. As highpockets has said Vectric has said 10 was coming soon & at the user group meeting which is 2rd October in UK they will be introducing people to what is new in V10 even if it hasn't been released by then. Might be worth waiting until then but only you can really decide. You could always download the trial version & have a look for yourself, that would really be the best way to see if it is worth you upgrading