Disclaimer: I work for a Trek retailer.
The Xcal 7 is certainly a pretty nice bike, with a nice drivetrain and brakes, and is definitely appropriate for cross country style riding for most people.
As mentioned by other riders, the biggest upgrade over the Xcal 7 would be something with an air sprung fork. This is a bigger deal if you're uncommonly heavy or light, as replacing the spring on a Rockshox fork is actually kind of costly. An air sprung fork can be set up to the appropriate spring rate for your weight and riding style. Additionally, an air spring will require progressively more force to compress as the fork moves through its travel, which can make the fork less likely to bottom out while still having good compliance to small and moderate sized inputs. The Xcal 9 is Trek's most affordable hardtail with an air sprung fork. The other major upgrade is running tubeless. Slightly nicer bikes (Xcal 8, for instance) will have tubeless ready rims, which will set up tubeless much easier and more reliably than the rims on the X7, and considerably nicer bikes will come with tubeless ready rims and tires, and just need to be set up. The difference in ride quality and traction from running quality tires tubeless is significant, in addition to self sealing most minor punctures. The rest of the bike is also really meaningfully upgraded as well, but that's what will make the largest difference to trail handling.
Any the bikes we're talking about will handle offroad way more aggressively than a cross bike (and I'm someone who loves tackling technical trails on a cross bike). It has to be mentioned that an entry/mid level hardtail isn't similar in downhill ability to a trail hardtail or full suspension bike, and if your goals are likely to turn to technical terrain and aggressive riding, it may be economically advisable to buy a trail bike if you're likely to want (and actually buy) a different bike down the line.