Duffy lists these remaining 3 regiments as Fusiliers, with fusilier style caps (not sure the pompons you mention necessarily indicate musketeer tricornes - coloured regimental pompons exist through the SYW for all musketeer, fusilier, and even grenadier companies). I ASSUME this indicates all wore fusilier caps, but despite searching have never seen anything confirming that.
The much later Regiments raised as 50-55 you mention have no relationship or lineage to the ex-saxon regiments other than the re-aplied number.
We can safely assume my comments about Fusiliers as 'lower cost' are down to drugs/poor memory/lack of sleep (I have a 4 week old daughter next to me as I type) but I'll go through my notes and see if I can find anything. Certainly they were issued the shorter, lighter muskets, and as a group their uniforms were much plainer and with less lace etc.
My comment on 2nd class citizens is refering to the fusiliers generaly being junior to the musketeer regts (based partly on SYW chef's, and the old dessaurs listings although they were not officially used through the SYW), and they are certainly in the SYW relegated generally to minor theatres, or placed in the 2nd line of battle (literaly).
Daryl