A correspondent writes about the use of to in such constructions as:
(1) I shall have to do more than (to) speak to him
(2) The new scheme will have to do more than (to) allow all women to....
(3) What I want to do is (to) go to Australia.
(4) (To) go to Australia is what I want to do.
He finds the to-less versions odd, especially in writing.
I don't have a problem with any of the to-less versions, actually. What we do have, I think, is a contrast of formality, with the to-ful versions more formal - and thus more likely to appear in writing. (A similar kind of contrast operates with the presence or absence of that in such sentences as I said (that) it would rain.) But the situation is complicated here by phonological factors. There is a euphony issue with a repeated to: many people don't like to do more than to speak and suchlike. Also there is a rhythmical issue with to do more than to allow, as the than to brings two unstressed syllables together, and this goes against the preference for iambic stress-timing in English, which is better preserved in more than allow. So I would expect acceptability intuitions to vary a little with respect to these examples.
If (4) feels odd (and I do find it a bit so), it is probably because of the unusual nature of the construction, seen in isolation. Within a discourse, with an appropriate intonation to express the emphatic contrast involved, I don't think the to-less version would attract attention. The version with to would be less likely, as (4) is plainly part of an informal exchange, and this would motivate the elliptical alternative.