Hmmm, a few more variables here and there.
The thing about car buying for your own personal use is that it's more of an emotion rather than a logical one. But I will also throw out the caution of not stretching your finances thin. If you're planning to do a smaller downpayment than 50%, I'll advice against your purchase and will advice you to get something less expensive. Something like a Toyota Vios will still ferry you from Point A to Point B while burdening your wallet less over the years.
I'll first isolate your sound system woes. I'll only peg the Rockford Fosgate system of the Lancer to be around Php15,000 to Php20,000. This isn't the market price but that's what I'll value it. It's not really all that "wow" but it's an added upgrade to normal speaker and it's the "OEM" factor that inflates the price.
For the car, I will advice you go for the Toyota Altis if you're worried about the depreciation value of any car. While the Lancer has maintained its value well, nothing will beat the thousands more Altis who'll soon be plying our roads. And since it's a major upgrade by Toyota, you're guaranteed you won't really be driving an "old" car soon.
I'll recommend the Lancer GT-A if you're thinking of "upgrading". The Lancer rides on a great chassis and the engine is easily one of the stars in its category even after factoring its age.
Between the two, I'll choose the Lancer. Why? The 2.0L powerplant is a gem whether it's for city driving or as a great base for adding performance parts. You should also take a look at Evo X wraparound kits which will really upgrade the aggressive ante the Lancer already has once you have thrown some performance modifications at it.
If you won't be the type to fuss about the depreciation - as in you plan on keeping the car for a long time, go for the newer Mazda 3. While initial costs might be quite high, you'll save up on its Yojin3 program over the long-run with a free 3-year service. But the two factors why this is ranks high on my list is: (1) engine and handling, and (2) build quality. Its Skyactiv engine with its Atkinson cycle engine is extremely efficient - not only does it have a lot of power but you have fuel efficiency to boot. Handling is the gem, until now I still find time to drive my sister's Mazda 3 from time to time. This is high praise since I own a
better car than hers

it's build quality is quickly approaching German-quality and that's something that should be
experienced.. rather than told.