Opinion - When is a good time to revamp a web application?

I am on a fence here on whether I should be revamping a web application that was developed for my organisation's website before I came.

Basically (without boring with the details) I am developing Application A and the higher-ups would like it to be intergrated with this other application called B which was created and used before I took over.

Now application B is about 1 year old now but it has some downsides and it was created very simply with no documentation whatsoever. I was planning to look over the code for B and upgrade some of its function etc to overcome the downsides it had. They were not major downsides but minor and annoying ones. B still did what it was suppose to do (in the higher-up's eyes).

Now as I am creating A and looking into how to integrate B, I realize I am gonna have to make alot of loop arounds etc to get it to integrate properly with B. Application B will also have to be modified semi-heavily to intergrate well to. And with those modifications the old data used by B will be invalid (which doesnt really matter).

Now after all tht, just based on that concept overall, I am inclined to just revamp B completely and re-create it from scratch myself since if I don't, I am just going to be building upon the old application B that I need to learn etc to fully understand it and to fix the fallback it has. Its kinda like building upon a foundation that is really not that great imho.

What is all your opinion? Hehe. Yeah I know I am kinda vague but I don't to be writing a 2 page story . Hope you guys get the main picture I am putting up here.

Thanks in advance for any opinions.

Think about the long term. Joining two programs to work together causes many problems. If you think building and maintance to join them together is goin to be higher than programming the whole things, then i would rebuild it. However if it seems like it is going to be esier to jus build from scratch then do that. Its a matter of opinion but i think a rebuild sounds good, unless it costs alot.

moved