Not every feature will be available in IPB and vice-versa. People need to have a balanced picture when choosing forum software.
You need to not only look at the annual cost (always work on permanent membership), but you need to look at phone support (if required), features that your members already use and can't live without, features which are new in the forum software you are looking at (that might compensate them for any lost features). Look at conversion costs, installation costs.
IPB will not be right for everybody - but it will be for many.
Look at the responses of staff - are they reasonable, do they appear pationate about the company they represent? Are fellow members quick to help and recommend? Do you get the truth even if that means 'sorry we are not the best option for you'?
Look at all options and then decide.
Some costs will be zero at IPB and others will cost - some costs maybe higher or lower than your current product - but weigh everything up. And if IPB can offer a refugee discount take this into account.
I am not going to bash any other product here, as I hold licences for UBB, VB, FusionBB & IPB. and would gladly move some of those sites here - so for me it is not just a VB issue, but if I can move more sites towards IPB then great - and I know I am not alone. I recognise several posts in the members section of different forum software.
Worth also mentioning that IPB have a business version - same product but comes with phone support and installation of not only the first install, but also upgrades plus a faster guaranteed response time on tickets. This might be suitable for busy sites, that perhaps require a greater link between you and Invision and are run as a business rather than a hobby.
I have been involved in forums for over a decade, so speak from experience - if I am not happy I say so and would not recommend s product that I was not prepared to sue myself.
Make your decision and if it is right for you and your members go for it.