I like that you're maintaining a well-loved and well-used H25. Small as it is, the boat is worth keeping!
I don't know why you mean to 'add wood' to the toerail extrusion, nor how you mean to do it. I agree with all that's said about the toerail, especially its versatility (having a toerail means never having to discompose the lifelines by hanging fenders from them!). It is also phenomenally strong and long-lasting. Consider painting it (use epoxy paint) when it gets scuffed up-- this will save it in appearance as well as in structural integrity.
Historical fact: the only Hunter 25 ever made without the aluminum toerail was Hull #1, which went to Skip Moorhouse, the sailmaker (c.1972-73). His had a regular teak toerail, bolted through the flange. (Also, Skip broke the mast while racing and ordered a replacement that he stepped in the bilge, making his the only H25 without a deck-stepped spar too; but though done at the factory that wasn't meant to be.)
I made number boards for my registration numbers that stand inside the toerail and get bolted through it. They're not on now because the pulpit is not mounted and the boat is under shrink wrap; but when I can I'll have photos. I meant to incorporate a chock in the aft end of these, for the bow lines, but found that mounting it on a block (to raise it so the lines clear the top of the toerail) was more hassle that it's worth. But I do not like having mooring lines or anchor lines led over the toerail-- their constant sawing will ruin the aluminum-- and support any idea, adequate aesthetically and structurally, that alleviates this.
In the end I have to agree with what Dalliance says (as I usually do

). You are considering adding a maintenance-intensive element, one that won't particularly add much in utility or appearance, to a well-executed design that's recognized everywhere for its simple lines and classic prettiness. Moreover, yours is a
series-1 boat, which (no offense meant to anyone else) I consider the best-looking of the H25 model range. Why mess with any of that?
As an aside, David mentions clipping snatch blocks to the toerail holes, which we all have done (and many see no reason to not do). However, these will make a real mess out of the anodizing in short order. Wichard makes a very expensive rubber-coated u-bolt meant to clip into the toerail (filling one hole, so, no movement = no scratching), but at over $100 each it's hardly worth it to most of us. For often-moved stuff, there are roller shackles, typically used for those mainsheet-bail systems, that might ease the pain on the aluminum, though in time they'll probably distort under weirdly-angled loads. Worth considering is a return to the concept of foot blocks, once you are satisfied with where your usual genoa and spinnaker sheetline leads should go. For the H25 or H27 I would recommend Schaefer 7-series cheek blocks (at the least), mounted aft on the coaming sides. These are rated at 2500 lbs; but remember a foot block's load is essentially double what the sheetline's load is because of the almost-180-degree turn (doubling back doubles the load); so make sure your backing blocks are adequate for heavy shear loads! The regular cheek blocks, just upsized, may be the cheapest solution. And they make the boat look cool as people notice that you seem to be a 'serious' racer in 'the old style', which to me is always the height of cool.
