New wheels for my Specialized Allez Expert Z2

Per the FAQ, we don't recommend specific products as they tend to become obsolete quite fast. We also don't really discuss product valuation. It's likely that the folks on Bikeforums, where you cross-posted, may offer some discussion on those aspects. However, general upgrade considerations can be a productive avenue for discussion here.

You have, with all respect, a lower-end rim brake road bike. Past a certain point, it's not really worth upgrading lower-end bikes. Bike manufacturers get favorable component (including drivetrain and wheel) pricing from manufacturers, because they buy in bulk. So, past a certain point, it's probably more cost-effective it to sell your bike to someone who wants an entry-level bike, and buy a new complete bike or a used bike.

Another thing to consider is that modern road bikes are increasingly shifting to disc brakes. If you had a disc brake bike and you bought a nice set of wheels, you might consider taking those wheels with you if and when you upgraded the whole bike (although you'd still want to consider the OEM pricing phenomenon discussed in the paragraph above). However, you have a rim brake bike. For performance road bikes, rim brakes may be a bit of a technological dead end. Many newer performance bikes don't have rim brake versions. Wheel and rim manufacturers might cease developing higher-end rims for rim brakes. That said, if you were willing to shop used, you might consider getting a used pair of nice wheels.

Discussing possible upgrades in my perceived order of cost-effectiveness:

• Upgrade to ultralight butyl tubes (you can keep the older butyl tubes as spares). These should reduce rolling resistance. You might even consider TPU tubes (currently, Tubolito is the only manufacturer, and they're very expensive) or latex tubes (they will lower rolling resistance even more than light butyl or TPU, and they may even be more durable, but they require daily inflation and can be tricky to install). Some independent parties have actually tested rolling resistance for inner tubes. Aerocoach published estimates for light butyl, TPU, and latex tubes. Bicycle Rolling Resistance did similarly, but I believe they also included some good standard butyl tubes.

• Upgrade to a high-performance road tire. Again, Bicycle Rolling Resistance and Aerocoach have published some estimates. Take note that Aerocoach focused on racing tires, and both outfits include time trial tires in their tests; those tires are very, very thin and not durable. High-performance tires like the Continental Grand Prix 5000, Specialized Turbo Cotton, or their equivalents from other manufacturers are good choices to consider here.

Those upgrades deal with consumable items anyway, and you could dismount the tires and move them if you decided to get a new bike. They will make a noticeable difference to the ride and to your perceived (and actual!!!) speed.

Upgrading your entire wheelset is trickier. You have a lower-end alloy-rimmed wheelset. I haven't been able to find exact specifications for your current set. However, you could get a used or new set of higher-end alloy wheels in your price range. The hubs might be more durable, and they would be lighter. Based on appearances, any changes in aerodynamics would be marginal. You have to make massive weight changes to see any meaningful differences in cycling performance.

You could consider getting a set of used carbon aerodynamic wheels instead. Those would make a noticeable difference. I haven't personally checked, but the used rim brake wheel market is likely to be soft, because the industry is shifting to disc brakes. However, carbon rims require special pads (emphasized because you will damage your rims and have poor braking otherwise), and braking will always be inferior to alloy rims. Moreover, if you ever did a ride with long descents, carbon rims are sensitive to heat, and can be destroyed if you drag your brakes too long (Google for carbon resins and glass transition temperatures if you're interested). I don't see this as a good idea for a lower-end rim brake bike, and I think this is out of your price range anyway.