First off... the XD wasn't designed by Springfield armory... it was originally called the HS2000. It was a croatian design and was imported from Croatia by intertec arms. I saw one of the original articles written on this gun by Guns and Weapons for Law Enforcement magazine. They stated that it had pretty bad accuracy, about 4 1/2 inch groups at 25 yards. They were impressed by a lot of the features on the gun though, such as a grip safety, loaded chamber indicator, etc etc. IMHO, accuracy is of chief importance, and I would be wary of such results.
Although, it is possible that since springfield armory obtained the rights to market this gun in the U.S., they may have improved the accuracy... I can't be sure since I have no information as to how the pistol proforms now versus that originl article. From my knowledge though, the design has not changed... so who knows.
As far as wanting a 9mm though... did you know you could by a 9mm upper for your Glock 23.
Glockmeister sells complete Glock 19 uppers. This G19 upper will fit perfectly on your G23 frame.... since they both use the same frame. This way, you could switch back and forth from a G19 config to G23 config. I would check it out if I were you. The complete uppers from Glockmeister cost about $360 I believe... this would be cheaper than a new or used XD. I would consider it if I were you.