I agree that a stepmother would have been useful if Valentine didn't have a paid housekeeper, sisters, aunts or mother/mother-in-law around to help, but I haven't seen any reliable evidence to point conclusively to Valentine having married Catharine Green after the death of Alles.
The lack of baptisms for two Valentines is not, for me at any rate, evidence that only one man was involved. I have several ancestors on my tree for whom I haven't been able to find baptisms despite much investigation by me and by others. Some of these missing records can be accounted for by damage/destruction, which I know to have taken place in the disruptive times in the 17th and 18th centuries (as for example occurred at Rivington Unitarian Chapel).
Do you know conclusively which of the following two Valentines here is which?
Burial: 13 Apr 1774 St Katharine, Blackrod, Lancashire, England
Valentine Whalls -
Abode: Blackrod
Register: Burials 1727 - 1782, Page 97, Entry 25
Source: LDS Film 2148001
Burial: 29 Jan 1780 St Wilfrid, Standish, Lancashire, England
Valentine Walls -
Abode: Blackrod
Buried by: Richard Perryn, Rector
Register: Burials 1772 - 1812, Page 26, Entry 12
Source: LDS Film 1526140
Burial of Alles (nee Orret) 13 May 1749 at Blackrod (from the LPRS):
Alles w Vallintin Walles
Valentine was left with a large family - the couple had 11 children baptised, including twins in April 1749. Acquiring a stepmother for the children would have been very important, even if there was help from relatives.
On an unrelated topic: I know you are interested in the name Donbavand. Are you aware of this record? I realise it may not be of consequence but thought I'd mention it after I found it when investigating Simm ancestors.
Marriage: 2 Aug 1759 St Oswald, Winwick, Lancashire, England
James Simm - this Parish
Jane Key - (X), this Parish
Witness: James Bankes; William Donbavand
Banns Read: 15 Jul 1758, 2nd: 22 Jul 1759, 3rd: 29 Jul 1759
Married by Banns by: John Lowe Curate