The feeling I find a bit worrying about this whole thread is that those who are opposed to renegotiating maintenance under any circumstances seem to think that the chilren from the first marriage have a "better" claim on any finances than the children from the second (or subsequent) marriage.
I have already said that I think fathers have a duty to keep up maintenance payments, as agreed at an appropriate level. FWIW, ex-wives also have a duty to state their costs at an appropriate level too, and I would also go as far as to say that they have a duty to spend it in the children's best interests (re: our shoe saga last year, not the only time similar has happened)
We could afford our children when we had them. Our situation has now changed - in more than one way - dh's job has changed and we have nowhere near as much money coming in, dh's ex has upped the costs by choosing one of the most expensive schools on the country for dss (a situation very possibly linked to knowledge of job change), and dd1 is needing more and more expensive treatments (and this does affect dsd and dss, as they want the best for their sister too, I suspect if we asked them whether they would prefer to go skiing 3 times this year or only go twice and give dd1 a chance to talk, they would choose the speech therapy option. But it is not a question we would ask)
Dh now has 4 children. Fact. All 4 of those children were born at a time when they could be afforded, and they would all have had an equal share of finances (ie we had as much money to spend as we are currenlty paying to dh's ex)if the situation had not changed. all 4 of those children are still entitled to an equal share of whatever finances are going. Dsd and dss are not entitled to a larger share because they were born into a first marriage. Therefore, it would not be unreasonable to renegotiate maintenance now.
In fact, were we to go back to court to change the order, we would most likely win. It is not worth the ill will from dh's ex, though, or the confusion and upset that it would create for dsd and dss, and so we continue in a situation that is not satisfactory.
No one is completley happy.
Dh's ex isn't happy, as she still thinks that dh has not "paid" enough for leaving (he did not, by the way, leave her for me, or in fact, for anyone, the marriage just slowly broke down).
Dh is not happy as he cannot afford to maintain a lifestyle that his children are comfortable to bring their friends into. It cannot be nice to be continually faced with the fact that your children think your house and lifestyle are shabby, or that they choose not to come on holiday with you because the holiday is not interesting enough.
Dsd and dss are not entirely happy because, although they have everyhting they could wish for in monetary terms, they do not feel able to fully share their lives with dh. they comparmentalise everything, because there is no way that dss would bring his friends form school to our lowly 4 bed semi, with a bathroom from circa 1970 and kitchen to match. It is sad that he is ashamed of us, but he is.