Bike Gearing Question

I think the upgrade to 10 speed is worth it - 105 components aren't that expensive (unless you're considering a new bike in the future).

However, if you're used to riding 14-28, an 11-23 cassette is going to be rough (no similarly easy gears).  Get a 12-25 or 12-27 and you'll be much happier.  Also, once you make the 10 speed upgrade, you can switch cassette sizes pretty easily, so you can get that 11-23 down the road if you feel you need it.  A cassette only lasts between 6 months and 3 years, depending on how much you ride. 

I would just check eBay for some used or NOS 7 speed cassettes if you are looking for some gearing options.  Unless you are running a compact crank then I would stay away from the 11-23 and instead look at something like a 12-25 or 13-26.  However, make sure you are carrying a small enough gear for the climbs on your course; running out of gear on a downhill is significantly better than running out of gear on an uphill.

I would not bother upgrading to nine or ten speed; the cassette is a relatively cheap addition and gives you different gearing options.  You would be better served to get the bike tuned up (learn to do this yourself) and saving money for a new bike down the road.

Shane

Even with good deals and upgrading the minimum he would be looking at:

Left STI - $75
Chain - $30
Cassette - $30
Rear wheel - $100

Plus labour, cables and housing and probably new bar tape.  This assumes that the RD will work with the setup (likely but not 100%) and that the wheel will fit in the dropouts (126mm vs 130mm spacing).  While if the frame is steel it could bend ot accomodate the rear but if it is alu, then I would not bend the frame even the 4mm to get the wheel in.

Shane

Assuming it would fit on your frame, SRAM makes an 11-26.

gsmacleod makes some very good points about what you would need to look into.
Another factor is to consider what you would give up gear wise to put a 11/23 on (if you go the complete conversion route)
You said you had a 14/28. I am not sure what all gears you have on that because shimano make a 12/28 and a 14/32 in 7 speed so you might have a 23, 25, 26, or 27 on there besides the standard 24 and 28 on a standard shimano cassette. by getting a 11/23 you are losing a 24 and 28 and quite possibly one of the other gears I mentioned above. YOu say you live in a hilly area and that you are around 200lbs. 3 gears with those factors would be something to consider. if you decide to make the change to 10sp maybe the 12/27 would be the way to go, you would get a 12 and 13 but you would keep a 24 and the 27 for climbing.

If you get a spare wheel with same cassette as you have on your current wheel you don't need anything else.

Don't bother changing to 9 or 10 speed but save your money and put it into your new bike fund as I suspect you have a new bike on your radar in the future.

Thanks for the suggestions everyone.

It's a tough call for me.  One one hand, I have no desire to get a different bike because I don't think the prices charged for them are worth it to me.  I like putting my money into assets that appreciate in value.  On the other hand, I see where you are coming from in terms of the amount of money I will spend on upgrading my existing bike.  At least now I know that if I do, I will go the route of the 12/27 cassette in order to keep some good climbing gears.