I have a Sora 2x9 front derailleur, and a Tiagra rear derailleur. I want to upgrade the Sora component. Do I need to be concerned about anything other than getting another 2x9 front derailleur? Thanks.
You need to be make sure the new front derailleur is compatible with your existing shifter and cable. If your shifter is Shimano, it's best to stay with a Shimano part for this one, to ensure compatibility.
I understand where you're coming from and the front derailleur shifting can be frustratingly marginal. If it's that frustrating you might look at going to 105 or even Ultegra, depending on the parts and price you find.
The (assumed) sketchy front shifting could also be a function of worn/bad cables and housing, and even shifter. It's probably worthwhile to replace that shift cable and housing as part of your upgrade. Or even try the shift cable and housing replacement first before upgrading the derailleur. Someone may have installed a less-than-optimal cable and housing for your particular derailleur.
If you really feel like going for it, you could get a new shifter too. But that's a slippery slope... of course you'd have to replace both shifters to match, etc.
In the meantime, you could find someone else who's really good with derailleur adjustments to try adjusting it one more and see if you get lucky... Just not whoever adjusted it last time! Worth a shot... The derailleur clamp positioning on the seat tube may have shifted enough to cause crappy shifting. If that's happened, the adjuster screws may not get the job done, and the clamp may need to be loosened and repositioned to get the cage in the right spot in relation to the chainrings and chain. Someone who is really good with these will usually spot that, as well as cable/housing issues.