I am not familiar with your current factory system, so I can not speak to what it has, or does not have for connectivity, but am familiar with just about all types of aftermarket gear...your brother is correct, they are much more advanced...
First off, the aftermarket will offer better connectivity options for Apple products, in addition to BlueTooth audio streaming from your iPhone wireless.
The "AUX" connection is great for those devices that do not have a Apple Dock connection, or BlueTooth streaming, but there are way better ways to connect today's modern devices. I have a single DIN JVC Arsenal DVD Dual-Zone head unit in my 4Runner, and I love the BlueTooth with my iPhone 4... No wires to connect, I can leave the phone in my jacket and still hear my tunes...
Depending on the stereo you choose, you have various ways of controlling your iPhone from the stereos interface - they will likely call this feature iPod or iPhone ready/compatible... Some have an awkward menu driven interface that take forever to scroll through your music collection if you have a bunch of music like I do... Some expensive ones have a really cool touch screen browsing feature, and others simply offer a USB connection that will digitally "handshake" with your Apple device to allow for charging and playing music while controlling everything from the device itself... Either way, most require a hardwired connection for this Apple compatibility...
Second, there is usually better support for navigation maps from aftermarket companies, as most car manufacturers here only cater to those in the continental USA, and perhaps parts of Canada... You may have to pay extra for the Dominican Republic if they offer it, but it would at least be an option...
They make all sorts of double DIN opening aftermarket head units that will fit where your current stereo is, and you have your choice of how much you want to spend for that.
If you already have factory mounted steering wheel controls for your OEM stereo, make sure you choose a new head unit that offers an interface to use those existing controls. If you do not have these controls already, some aftermarket units do offer some sort of "remote" option. Most common is a wireless remote that comes standard, like mine did. But this is like any other remote control you would have for a home stereo - it takes batteries, gets lost, and is not mounted to your steering wheel. Some offer traditional hardwired "steering wheel" remote controls, but I have no experience with using these, and some have pretty small buttons that could be a pain if you are going on tactile feel alone.
After all this, you would still have to choose at that time to upgrade the rest of the system or to stick with the stock amplifier, speakers, and sub-woofer (if it came with one). Not to mention the purchase of adapters and interface products you would require to stick with those stock items. Again, not being familiar with what you have already, I can't say if you should keep it or not as per your music needs and tastes... However I will say, that just like the head unit, you have WAY better selection and quality options in the aftermarket - you will just want it designed and installed correctly.
My entire system, including power distribution is completely independent of anything the OEM truck came with. I did not even reuse the factory speaker wires, as I wanted to upgrade to bigger wire. The only OEM item I did re-use was the factory power antenna system...
Not sure if I answered any of your questions, but hopefully I gave you some insight into what your options are like in the aftermarket...