Want Slightly Louder Exhaust Without Changing Much

You don't need bigger to get a better tone, nor to you gain instant power.  Unless you have upgrated something to increase airflow a larger diameter exsaust is not going to gain a lot.  Infact you gain a droning sound in the cab.  These cars a quite with no mufflers, they just get a bad raspy sound. 

If you want a more agressive sound replacing the muflers with resonators or glasspacks would help mild down the raspy sound yet you will gain a more agressive sound when you step on it.  It might gain you some power since the exsaust will have a more unobstructed path.  Supersprint made a nice exhaust sytem back in the day.  I have an original set and if you type supersprint in the search you can read all about it.  The sound is like an early european sports car.   Basicly the system used the same diameter exhaust with:

one resinator at 12" long, with inlet and out let at 1.75"

the two over under resinators in the back at 12" long with inlet and out let at 1.5" 

The pipe follows that same as stock except the Y added to the rear resinators.  Then they welded 2" chome pipe

1.75" diameter pipe has a aproximate flow area of 2.41sq"

1.50" diameter pipe has a aproximate flow area of 1.77sq"

1.5" pipe times 2 is 3.53sq"  this falls close to a 2" pipe, but less that a 2.25"

Just for kicks I priced the resinators online in stainless steel I found the 1.5" for $11.45 each and the 1.75" for $13.74.  Highend conectors (so you can take it apart) $2.50 each times 2 for $5.  One Y conector $2.50.  With new pipes from the downpipe back with 4 bends, last I checked a shop charges $20 a mandrill bend. About $40-$45 of pipe (stainless of course).  6-8 weld about $10 each.  one can of exahst spray paint $12. and lastly two chrome tips for $25 (got to have the bling).  Plus hanges I forgot to price them.  You can replicate the system.