wondering if is it worth buying garmin fenix 5, or just wait for the new model???

The 5 is a year and a bit old by now. There may be a newer model early next year.

Buy now or wait? To a large extent that depends on your situation, how much you want the watch now, whether you are expecting/hoping for any new functionality that only a newer model can deliver.

I haven't seen any rumors of an impending new Fenix release.

Fenix 3 was announced at CES in January 2015, Fenix 3 HR was announced in January 2016, Fenix 5 was announced in January 2017 and released in March 2017. No new Fenix's were announced in January 2018. If Garmin were following the same schedule (and that's a big if), you'll probably be waiting 10 months.

While it is likely that the next Fenix will include music and Garmin Pay (as the recently released Forerunner 645 has), it's not clear what else might be included.

Here is what you can expect feature wise, at least for now. https://www.dcrainmaker.com/2018/05/connect-tidbits-features.html

Certainly more metrics surrounding HRV/RR would be an obvious advancement. I am guessing that there will be music and non-music options as the former will take up resources (storage, battery drain) that may compete with high end features. But a year is a long time in hardware development, so I am sure there will be surprises. Resale values are generally high, so if you really want a watch now, go for it and sell it if you think the features and price differential are worth it next year.

Had the same quandary myself..... then I found the Sapphire Kit reduced to under £500 so it was a case of grab it while its cheap.

I thought I'd not like not having a touchscreen but I've gotten use to it now - although occasionally I have thoughts on that!

More memory would be great, whether its for music or just adding widgets and clock faces.... my biggest fear (which may be unfounded) is that as you load up faces and widgets that the watch will slow down and struggle.

I'm not impressed with Floor Counting (no biggie), its pretty much useless at it!!
Bluetooth Connection is very much hit and miss. Setting it up is easy, but the watch constantly disconnects from the phone even when the phone is in my pocket. I get Bluetooth has limitations, but when it disconnects at such short ranges, and as much as it does I feel there are issues!
The App needs much improvement too, but that affects any Garmin you get.

But that aside, its a good bit of kit. If you can get it cheap its even better.

By it online and you'll get anywhere between 15 to 30 days to return if you're not happy, but once you start playing with it its hard to take off.

I must have lucked out as I dont get BT issues, in fact my connections pretty strong. :)

After 3 months of watching YouTube reviews of the Fenix 5 and waiting CES to see the next model (that didn't appear), I've found on eBay, at 350€, the Silver Fenix 5 and purchased it. I was expecting a lot of problems with it, after seeing a tone of people complaining about their watches, but FORTUNATELY, mine is working as it should. Just some altitude glitches from time to time (2-5 meters), but I saw that it calibrates it self from time to time. Other than that, I'm happy with it!
After using Fitbit for 5 years and using Fitbit Ionic for 5 months, I can say that Fenix 5 it's a step up in terms of GPS, accuracy and battery life. I don't miss having music on the watch and I really love that now I can use a chest strap (Polar H10) with my watch for better and more accurate strength training, bike and run metrics.
If you find the Fenix5 at a reasonable price, in my opinion, you could buy it without regretting it.

Here is what you can expect feature wise, at least for now. https://www.dcrainmaker.com/2018/05/connect-tidbits-features.html

Certainly more metrics surrounding HRV/RR would be an obvious advancement. I am guessing that there will be music and non-music options as the former will take up resources (storage, battery drain) that may compete with high end features. But a year is a long time in hardware development, so I am sure there will be surprises. Resale values are generally high, so if you really want a watch now, go for it and sell it if you think the features and price differential are worth it next year.

Actually, my guess is that they will all offer music, as it won't take storage or use battery if you don't use it - people may use music on a training run, but not on an ultra. (No inside knowledge here, just speculating).

Finally, the update for fenix 5 has come out. But there is not much innovation that dominates me. How do you think, there is a chance that a new model will appear in 2019? Because the fenix 5 is better than the phenix 5 plus by the price. How do you think if sleep monitoring is better in the future, or Fenix 5 will get it, talking about sleep apnea, etc.
The next question is which one is better whether Fenix 5 or Fitbit ionic: by sleep tracking; activity tracking, sports tracking; weight lifting sports?

Would not touch a Fitbit with a 10 ft. pole. Had one, and they are barely splash proof. Was out on a hot humid day, and it fogged-up under the glass, and was never right again.

Comparing a f5 to a fitbit? You know at times they give away fitbits if you buy enough breakfast cereal, right? I used fitbits for a while, and the workmanship and quality of the HW was pretty bad in my experience.