Hi Mr D
If you are purchasing handtools with a small budget in mind (a relative statement I am aware), then LN (or LV or Philly or a number of others of similar ilk) are probably not the way to go. When you extend the choice of tools to "rough" work, then my advice would always be to buy and fettle up a vintage Stanley. LN are very fine planes and too good for rough work (unless your finances are not an issue - but here you state that the LN is a special purchase).
The #5 and #5 1/2 are traditionally for rougher work. They are an interesting inclusion in a set of tools if one is setting out to upgrade handplanes and does not already have a quality smoother (I disagree with those who argue that a #5 is great as an all-rounder - it is an all-rounder, but eventually one will want to set it up for a single specialisation). It is really only the likes of David Charlesworth that have pushed for their uses as a "super" smoother. I have no problem with that - it perfectly suits those that prepare their boards on machinery (= relatively flat) than by hand (a short smoother will preserve the thickness better).
All LN's are just tools. Use them like any other tool you own. That is what I would do, but I only work in a workshop where my tools are welllooked after. If I was also on a worksite, and this was a special plane, I would be tuning up the #5 as a smoother for the personal projects, and using one of the older planes for the worksite.
Regards from Perth
Derek