As it is a CR51 i reckon it has the 2c engine, that model was particularly underpowered.. First take a look at your engine, high chance that I maybe needing attention also the fuel pump, other than that the 4wd is a very good option, it has a lot of traction quite useful in the hilly areas, No issues at all with the 4wd system also, but I have done an engine upgrade.
I don't see a difference in the fuel economy, I've been having one since 2002, still going strong, If you really wanna see the difference take the front prop shaft off, and take it for a spin.. It doesn't do much, btw make sure you put it back on afterwards
People here think that AWD is like running a 4wd select vehicle in the 4wd High range all the time,
so they've made it up as if the parts wear off too fast, and the fuel consumption is high and all that,
But manufacturers consider all these before making an AWD.. I'm sure you are on this impression too..