To Sequel or not to Sequel, a question?

One of my very first books was short, odd, difficult to read and many found it strange. Yet over years it found it's own market place and flourished. Meanwhile I had found a very comfortable niche and prospered selling books in small quantities but steadily and at a reasonable level in other genres. Yet that very early book has continued to sell and I have been asked many times over the years for a sequel. Normally (in pursuit of money) I would put my worries aside and accede, especially when being offered a substantial advance.

Yet in this case I hesitate, the original book was unique or at least different from all that I have read. I suspect that it's "oddity" is what makes it attractive. So I would have to write something just as odd but just as enchanting. I can easily do either on their own but together?

To make matters worse another author has already written a sequel to my book and my own publishers are seriously considering it.

So what do you think? Should I go for it and hope to match my old creation, not jeopardizing my current sales or just go all out there and write the sequel? Any advice will be appreciated.