I am currently testing out the TSIACPatch and have Kachicko and Nalia in my party. My tentative plan is to keep Kachicko and drop Nalia when I can pick up Imoen however, I see Kach. as a buff then kick butt frontliner and it might be a waste to have her memorizing a lot of stand in the back and toss spells. Any thoughts?

You can always unlearn and relearn spells.

Sorry, I don't get your point here, Iroumen.

Nazar's question is whether he should let Nalia write some of those relatively rare scrolls (such as Ray of Fragmentation, Hand of Undoing, etc) in her spellbook or is to betterto give them to Kachiko who is a permanent party member. His point is that since he is eventually going to drop Nalia, is it wise to give rare spells to her?

On the other hand, Kachiko (as a Kensai-mage) is mostly engaged in close combat and may not be able to cast spells as freely as Nalia can.

Nazar asked this question in the workroom too and my suggestion was to give prioirty to Nalia only for spells upto 6th level. Since Nazar wants to replace her with Imoen, Nalia will not stay in the party long enough to need to know high level spells.

I thought that he meant that either mage is restricted in the amount of spells she can memorise, and that he was contemplating whether he would learn kachiko protective or offensive spells.
So my reply (though admittedly cryptic) implied that you can learn protective spells you need now and unlearn some of those spells when you want to change to offensive casting... then unlearn some offensive spells again and relearn the protective spells, and so forth.

I think it would be logical that you memorise the rare scrolls only for the mage that you take with you all the way through the game.