Other than that, yes, HIIT is an effective cardio protocol, and much research has shown that intensity matters when it comes to cardio.
What's discounted here is the full picture of fitness and training: cardio alone isn't sufficient, especially as you leave your 20s and 30s and suffer age-related muscle loss (sarcopenia).
The pretty cool thing about effective training programs is that significant gains, and certainly maintenance of a pretty high level of performance, can be attained on fairly minimal training. Three times a week, 10-20 minutes of cardio, and 30-40 minutes of lifting (less if you stick to big compound lifts) can do a huge amount for general fitness. Some abilities take longer to train -- especially skill sports. But the body is amazingly adaptive to constructive stress.
For 2 months I've been doing 50 minutes of cardio M-F at 6AM before breakfast, before work. So far I've lost about 12 lbs, but most importantly my energy level and focus throughout the working day is vastly improved.
I would like to incorporate strength/weight training into my routine. What would be the best way to go about this? Do I have to stop doing the cardio? Can I do both (as I would prefer to)? Can you point me to some good routines to get started? I posted on /r/fitness but didn't really get any valuable responses.
Another good basic primer: http://www.liamrosen.com/fitness
If you're looking for a good solid strength program, buy Mark Rippetoe's Starting Strength and do the program.
A slightly more varied, and less hardcore program is in Schuler & Cosgrove's The New Rules of Lifting. I find the texts complementary. SS has the better (IMO) beginner's program, TNROL has more complete information on overall fitness and diet.
SS is also going to benefit more from access to a proper gym with power cages, chin bars, and bumper plates (ideally). TNROL can be done largely at home with fairly a bit of equipment.
Once you pick a program and start doing it, re-read the FAQs and basics, then post any specific questions you've got to a decent forum (/r/fitness is pretty good).
No need to give up cardio completely, just swap it for a few strength training days.