OOE was more polished, but it wasn't a new style. It didn't take the game in a new visual direction, which it desperately needed.
Granted in handheldvania certain sprites were inevitably recycled or reanimated so they were reused in some way.
But how are you defining 'style':
"a distinctive appearance, typically determined by the principles according to which something is designed"
Specifically based upon appearance/ graphics?
If so, I'm not really certain I understand this concept, Mario for example, the 2d games' style doesn't seem to have changed aside from going 2.5D. The 2.5D "style" looks pretty well the same as it did in 2d (Example of Super Mario World compared to Super Mario U/ Luigi U) aside from the HD factor.
Castlevania tried the same thing with MoF, look how this turned out? Even if anyone likes the visuals (which were uninspiring to say the least) the engine impacted the game horribly and didn't work. Visually and stylistically the game no longer resembled nor felt like Castlevania.
The only game that specifically springs to mind that specifically has reinvented itself evolving graphically and so distinctively so over the years is The Legend of Zelda. Interestingly enough with the release of TPHD, it's supposed to be a "graphical evolution" from TP, yet they've removed much of the bloom lighting and ambience that gave the game its atmosphere in the first place. It's new "clean" appearance just leave it looking slightly more textured but a bit more dull imo.
One can argue that a series such as MGS has "evolved" graphically to the point of realism, but again I ask is it evolution simply because the graphics are higher resolution? MGS has nice graphics, but this was exactly the way I felt about MGS when I saw MGS for PS2. Has it evolved?
The problem with Castlevania's graphics evolving like Mario or Contra is that it's hard to capture the feel or atmosphere of an environment in 2.5d. With sprites you can make things look old, decrepit, ancient, architectural. I'm not so certain this is possible with 2.5D and I've personally never seen a game that's done it really well. Contra's graphics are actually too colourful and spritely imo for a Castlevania game, and I don't believe the 2.5D works. DXC's graphics did not look any better or more "evolved" from RoB's imo, even if we only count the backgrounds without the characters.
The way I define "style" is the aesthetic, ost and "feel" - ambience, gameplay, environment etc - of the game. In this sense OOE did much for the franchise, with refined Metroidvania gameplay, polished and attractive graphics, exceptional OST. Graphically for a handheld the game was good, for whatever budget it was made on it's one of the more attractive DS games (2d or 3d imo). It was also one of the more colourful Castlevania handhelds, the graphics were very clear and crisp, yet it managed to not over do it and still gave that certain ambience which the series has always carried. That's why I'm saying it was an evolution from the previous games. Graphics and graphical style play a much larger role in the Symphony that is Castlevania.