yeah, i tend to agree with the mdf ring spacer idea. i used it as well...but mainly because i had to.
i orginally replaced my speakers with diamond audio m series and eclipse components up front. i used 1.5 inch spacer from metra. but i personally found that you couldnt crank them down to the door internal panel very well...and they vibrated alot.
while shallow speaker would allow for you to not use a spacer, well...frankly for anyone with an ear for good sound, sound better then the orignal factory speakers, sony xplods are not the way to go. no disrespect meant, but they are the generic of speakers, if your gonna buy a tv, but a sony, but in car audio...spend a little more online. and get something nice.
the one nice thing about sonys is that they might run better off your original stereo because they really dont require alot (or could handle) a high amount of rms power. your factory vw radio pushes roughly 11 watts rms. if you bought a good set of speakers, like polks, or pioneer tsd series or diamond audio or eclipse or mb quart, they would require at least an aftermarket stereo that pushes 20+plus watts rms per channel. or better yet an aftermarket amp...which for anyone that just doesnt need sound...but good sound...is the way to go.
beyond all that the car is not set up well for good sound, the compartments for the speakers dont separate the front wave from the back wave very well(esp in the rear panel) and in the fronts the entire cavity of the door is the air space for the speaker...which is more then most 10 inch subwoofers require...which is to much for a 6.5" (basically that means its tough to get "good" bass from any replacement speakers)
as far as your radio goes....9 years of life is decent for a factory radio....but keep in mind what happens to your windows when you get in your car and its cold out...they fog up...that same condensation builds up on the inside of you radio...eventually its gonna die. so id expect to replace that sooner then later. in numerous threads ive made many suggestions. but the one i like the most is a kenwood. especially for the money, it is ipod capable, it has a five line display for searching the ipod, 3 band eq, time correction(which prob is the most important for the beetle), and high voltage preouts for any amps you decide to add. i have this radio and my only complaints are the knobs...they are a little touchy...but you get used to it and it comes with a remote too. and i wish the volume levels were more minute, i believe top volume is only 35....so each increment is a pretty big difference. i wish it were more like a pioneer or alpine or eclipse where they go to 70 or 80. therefore having smaller volume increments. (oh and it actually looks decent in the beetle. it has a symetric design and lights up with blue and red lights, with a white readout.
heres my suggestions....basically the cheapest route without comprimising good sound....if you go this route i promise the only thing youll wanna change someday is maybe adding a sub. but you wont be unhappy...
radio:
Kenwood KDC-HD942U (kdchd942u) All In-Dash Car Stereo Receivers Car Stereo Receivers and Head Units Car Audio Car Audio, Video, & GPS Navigation - Sonic Electronix
rear speakers:
Pioneer Premier TS-D602P (tsd602p) 6-1/2" Speakers Car Speakers Car Audio Car Audio, Video, & GPS Navigation - Sonic Electronix
front speakers:
Pioneer Premier TS-D720C (tsd720c) 6-3/4" Component Systems Car Speakers Car Audio Car Audio, Video, & GPS Navigation - Sonic Electronix
and amp if you wanna go top notch
by the way...insanely great product, and rediculous price)
Diamond D6700.4 Car Audio D6 Series 4Ch 700 Watt Speaker Amplifier (D6 700.4)
thats just the way id do it.
i have that amp and that stereo, i spent a little more on my speakers thou. i have mb quart premiums, while i love them i really dont think in the beetle and its physical speaker locations and limitations they are any better then the pioneer tsd series. (except for maybe the tweeters and crossovers are a bit better, but not worth the expense...in my opinion)
also the above links are just for example...you can search those products elsewhere for better prices....but i know you wont find a better deal on the amp....its a crazy good amp, even thou its sizeable, it would actually be able to run 4 speakers bridged on two of the channels, and the other channels could run a decent sub.
this of course is all advice if your picky about your sound....its a difficult car to get sound out of...especailly at 65 or 70mph with the windows open.
oh and the tsd series i linked are the premier versions, which are a tiny bit more expensive(at least in stores) then the regular pioneer series, but its basically the same product, just with a longer warantee.
good luck with whatever you do, let me know if i can help anymore, and sorry for all the misspellings.