The first part of verse 9 indirectly quotes Lehi’s words as “my father saith that he should baptize in Bethabara beyond Jordan”. Joseph Smith edited the historical present saith to said and deleted the that. Later on in the verse, he edited the verb spake to said in addition to again deleting the that. All of this editing is of a secondary nature. Joseph probably changed the verb from spake to said because of the adverb also, thus increasing the parallelism between the two indirect quotes (that is, “and my father said … and he also said”). For discussion of the change from saith to said and the deletion of the that, see historical present and that in volume 3.
As far as the change from the verb speak to say is concerned, this is the only place where Joseph Smith made such an editorial change. His editing here is characteristic of his early attempts to smooth out the text. There is nothing grammatically wrong with “and he also spake that he should baptize with water”. Other examples of this usage have not been removed from the text. In the following passage, we have an earlier example of an indirect quote where the verb is speak rather than say:
In this example, however, the previous verse (1 Nephi 4:23) uses the verb spake (“and I spake unto him as if it had been Laban”), so there was no need here to change spake to said.
Summary: In 1 Nephi 10:9, restore the original spake that Joseph Smith edited to said; Joseph’s editing here is an attempt to increase the parallelism of the text.